JP7676378B2 - Aluminum alloy with improved extrusion and corrosion resistance - Google Patents

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 62/925,314, filed October 24, 2019, the entire contents of which are incorporated herein by reference.

This disclosure relates to aluminum alloy-based extruded and brazed products and methods for their manufacture.

Aluminum alloys provide corrosion resistance to manufactured parts and are used, for example, in the automotive industry as well as in heat exchangers and air conditioning applications. They are used for piping because they provide moderate strength while being light weight with good extrudability. Long-life corrosion-resistant alloys have typically used high Mn contents or Ti additions, which are detrimental to extrudability and can reduce extrusion speeds and die life. Improving extrudability without hindering the long-life corrosion-resistant performance of this alloy is a challenge. Improvements are needed.

The present disclosure relates to aluminum alloys having improved extrusion properties, and aluminum products containing same having improved corrosion resistance.
In a first aspect, the present disclosure provides an extruded and brazed product comprising an aluminum alloy comprising, in weight percent, Mn 0.6-0.75; Fe 0.11-0.16; Si 0.10-0.19; Cu <0.01; Zn <0.05; Ti <0.05, with the balance being aluminum and unavoidable impurities. In the extruded and brazed product, less than 15% of the width of the product comprises coarse recrystallized grains. In one embodiment, each of the unavoidable impurities is present at a maximum of 0.03, with the sum of the unavoidable impurities comprising less than 0.10. In another embodiment, the aluminum alloy comprises Ni less than 0.01. In yet another embodiment, the aluminum alloy comprises Mg less than 0.05. In yet a further embodiment, the aluminum alloy comprises Cr less than 0.05. In yet another embodiment, the aluminum alloy comprises Mn 0.64-0.72. In still further embodiments, the aluminum alloy includes 0.11-0.14 Si. In some embodiments, the aluminum alloy includes 0.12-0.16 Fe. In additional embodiments, the aluminum alloy includes 0.011-0.024 Ti. In some embodiments, the extruded and brazed product is extruded and brazed tubing, such as, for example, micro-multiport tubing.

In another aspect, the present disclosure provides a method for producing an extruded brazed product. First, a billet is provided that includes an aluminum alloy, the aluminum alloy having, in weight percent, Mn 0.6-0.75; Fe 0.11-0.16; Si 0.10-0.19; Cu <0.01; Zn <0.05; Ti <0.05, with the balance being aluminum and unavoidable impurities. Next, the billet is homogenized by at least one heat treatment. The billet is then extruded into a product, and the product is brazed to obtain the extruded brazed product. The method may further include casting the aluminum alloy into a billet prior to providing the billet. In one embodiment, the method further includes cooling the billet after homogenization and prior to extrusion. In one embodiment, each of the unavoidable impurities of the aluminum alloy is present at a maximum of 0.03, and the sum of the unavoidable impurities is less than 0.10. In one embodiment, the aluminum alloy includes less than 0.01 Ni. In another embodiment, the aluminum alloy includes less than 0.05 Mg. In a further embodiment, the aluminum alloy includes less than 0.05 Cr. In yet a further embodiment, the aluminum alloy includes 0.64-0.72 Mn. In yet another embodiment, the aluminum alloy includes 0.10-0.14 Si. In yet another embodiment, the aluminum alloy includes 0.12-0.16 Fe. In yet another embodiment, the aluminum alloy includes 0.011-0.024 Ti. In one embodiment, the extruded and brazed product is piping, such as, for example, micro multiport piping.

In a third aspect, the present disclosure provides an extruded brazed product obtainable or obtained by the method described herein.
Many additional features and combinations of the improvements according to the present invention will become apparent to those skilled in the art upon reading this disclosure.

FIG. 1 is a graph of dispersed particle volume fraction as a function of soak time (hours) for three aluminum alloy compositions (Fe and Si contents are indicated in the figure legend). FIG. 2 is an example of standard alloy AA3012A exhibiting coarse recrystallized grains throughout the outer wall thickness. FIG. 3 shows the surface of the sample of FIG. 2 after macro-etching, showing coarse recrystallized grains on the surface. 4A shows the surface grain structure revealed by Poulton macroetching of different tubes from a commercial run: the material on the left is the "as extruded" tube, the material in the middle was subjected to a simulated brazing thermal cycle at 605°C for 2 minutes, and the material on the right was subjected to a simulated brazing thermal cycle at 605°C for 4 minutes. 4B shows the surface grain structure revealed by Poulton macroetching of a brazed tube from a commercial run. The material was subjected to a simulated brazing thermal cycle at 625° C. for 4 minutes.

The present disclosure relates to an Al-Mn-Si-Fe extrusion alloy with improved extrudability, as well as to products containing the same that exhibit long-life corrosion resistance. The disclosed aluminum alloy exhibits improved extrudability. Extruded and brazed products made from the disclosed alloy exhibit a fine post-braze grain structure and/or resistance to extended homogenization and brazing cycles. As used in the context of the present disclosure, the term "fine post-braze grain structure" refers to a structure that consists primarily of residual fine grains generated during the extrusion process and that is correspondingly free of coarse recrystallized grains formed during the brazing cycle. The expression "fine as-extruded grain structure" refers to a structure that consists primarily of residual fine grains generated during the extrusion process, prior to any brazing cycle. Further according to the present disclosure, "coarse recrystallized grains" means grains with a width greater than 200 microns across the extrusion plane (i.e., perpendicular to the extrusion direction) or a thickness that extends through the entire outer wall thickness of the tube. Figure 2 shows an example of the grain structure of alloy AA3012A after sizing and brazing, where coarse recrystallized grains are present extending through the entire wall thickness. Figure 3 shows the tube surface appearance of the same sample as in Figure 2 after macroetching, where coarse recrystallized grains with widths greater than 200 microns are present on the tube surface.

The alloys of the present disclosure are particularly useful for making extruded (e.g., aluminum) products. "Extruded aluminum product" means a product made from an aluminum alloy of the present disclosure that is forced through a die at an elevated temperature to obtain a desired cross-section.

The extruded aluminum products of the present disclosure are brazed to other components, for example to create heat exchangers. "Brazing," as defined herein, is the process of metallurgically joining two or more articles by melting and flowing a braze metal into at least one joint. A "brazed product" is defined as one that has been subjected to brazing.

As shown herein, the chemical composition of the aluminum alloys disclosed herein is advantageous in maintaining a fine post-braze grain structure in the outer wall of the product (e.g., tube), thus preventing or limiting recrystallization or "coarse grain formation" during brazing at high temperatures. Recrystallization at this stage replaces the desirable fine grain structure resulting from extrusion with a coarse grain structure in which one coarse grain may occupy the entire wall thickness of the tube. This condition provides a direct corrosion path through the material and is detrimental to the corrosion resistance of the piping. Therefore, recrystallization to coarser grains needs to be avoided, prevented, or limited.

In a first aspect, an aluminum alloy is provided that includes, in weight percent, about 0.6 to about 0.75 Mn; about 0.11 to about 0.16 Fe; about 0.10 to about 0.19 Si; less than about 0.01 Cu; less than about 0.05 Zn; less than about 0.05 Ti; optionally a grain refiner; and optionally less than about 0.01 Ni, with the balance being aluminum and unavoidable impurities.

The aluminum alloys of the present disclosure are Al-Mn-Si-Fe alloys and therefore contain Mn. However, the Mn content of the aluminum alloys of the present disclosure is lower than the standard corresponding "long life" Al-Mn-Si-Fe alloys. This reduced Mn content results in lower flow stress and improved extrudability. Mn is also important for the formation of Al-Mn-Fe-Si dispersoids and for enhancing self-corrosion protection with adequate mechanical strength. Mn is present in the aluminum alloys of the present disclosure in an amount ranging from about 0.6 to about 0.75, from about 0.61 to about 0.74, from about 0.62 to about 0.73, from about 0.63 to about 0.72, from about 0.64 to about 0.71, from about 0.65 to about 0.70, from about 0.66 to about 0.69, from about 0.67 to about 0.68, from about 0.6 to about 0.74, from about 0.6 to about 0.73, from about 0.6 to about 0.72, from about 0.6 to about 0.71, from about 0.6 to about 0.70, from about 0.6 to about 0.69, from about 0.6 to about 0.68, from about 0.6 to about 0.67, from about 0.6 to about 0.66, from about 0.6 to about 0.65, from about 0.6 to about 0. 0.64, about 0.6 to about 0.63, about 0.6 to about 0.62, about 0.6 to about 0.61, about 0.61 to about 0.75, about 0.62 to about 0.75, about 0.63 to about 0.75, about 0.64 to about 0.75, about 0.65 to about 0.75, about 0.66 to about 0.75, about 0.67 to about 0.75, about 0.68 to about 0.75, about 0.69 to about 0.75, about 0.70 to about 0.75, about 0.71 to about 0.75, about 0.72 to about 0.75, about 0.73 to about 0.75, about 0.74 to about 0.75, or about 0.64 to 0.72 weight percent.

The aluminum alloys of the present disclosure also contain Fe, which is beneficial in enhancing resistance to coarse recrystallized grain formation after homogenization. Fe also plays a role in controlling the distribution of Al-Mn-Fe-Si dispersants. In addition, Fe reduces the solubility of Mn and promotes the formation of Al-Mn-Fe-Si dispersants. However, excessive levels of Fe can be detrimental to pitting corrosion resistance by creating active cathodic sites. Fe may be present in the aluminum alloys of the present disclosure in a weight percent of about 0.11 to about 0.16, about 0.12 to about 0.15, about 0.13 to about 0.14, about 0.12 to about 0.16, about 0.13 to about 0.16, about 0.14 to about 0.16, about 0.15 to about 0.16, about 0.11 to about 0.15, about 0.11 to about 0.14, about 0.11 to about 0.13, or about 0.11 to about 0.12.

The Si present in the aluminum alloys of the present disclosure promotes the formation of Al-Mn-Fe-Si dispersoids and contributes to the distribution of the Al-Mn-Fe-Si dispersoids. In addition, Si reduces the tendency for the volume fraction of the dispersoids to decrease with extended homogenization times. As shown in the examples, it has surprisingly been found that Si provides significant control of post-braze grain structure under severe processing conditions to obtain desirable low recrystallization. However, excessive Si levels can reduce the bulk melting point of the alloy, reducing extrudability. Si is present in the aluminum alloys of the present disclosure in an amount from about 0.10 to about 0.19, from about 0.11 to about 0.19, from about 0.12 to about 0.19, from about 0.13 to about 0.19, from about 0.14 to about 0.19, from about 0.15 to about 0.19, from about 0.16 to about 0.19, from about 0.17 to about 0.19, from about 0.18 to about 0.19, from about 0.10 to about 0.18, from about 0.1 1 to about 0.18, about 0.12 to about 0.18, about 0.13 to about 0.18, about 0.14 to about 0.18, about 0.15 to about 0.18, about 0.16 to about 0.18, about 0.17 to about 0.18, about 0.10 to about 0.17, about 0.11 to about 0.17, about 0.12 to about 0.17, about 0.13 to about 0.17, about 0.14 to about 0.17, about 0.1 0.5 to about 0.17, about 0.16 to about 0.17, about 0.10 to about 0.16, about 0.11 to about 0.16, about 0.12 to about 0.16, about 0.13 to about 0.16, about 0.14 to about 0.16, about 0.15 to about 0.16, about 0.10 to about 0.15, about 0.11 to about 0.15, about 0.12 to about 0.15, about 0.13 to about 0.15, about 0. It may be present in a weight percent of about 0.14 to about 0.15, about 0.10 to about 0.14, about 0.11 to about 0.14, about 0.12 to about 0.14, about 0.13 to about 0.14, about 0.10 to about 0.13, about 0.11 to about 0.13, about 0.12 to about 0.13, about 0.10 to about 0.12, about 0.11 to about 0.12, or about 0.10 to about 0.11.

The aluminum alloys of the present disclosure may, in some embodiments, include Cu. However, because Cu can reduce self-corrosion resistance, the Cu content, if present, is limited to less than 0.01 wt.%.

The aluminum alloys of the present disclosure may include Zn in some embodiments. Extruded tubes for heat transfer applications are often coated with a galvanic sacrificial layer of Zn. The Zn may be deposited by arc spraying or plasma spraying with a Zn-containing flux, and the Zn diffuses into the tube surface during heating to brazing temperatures. The Zn concentration in the base alloy is limited to less than 0.05 wt.% since Zn can interfere with the behavior of the sacrificial coating when present in high concentrations.

If desired, a grain refiner may be included in the aluminum alloys of the present disclosure in the form of Ti, TiB, or TiC to solidify the aluminum alloy with a fine grain structure that is perfectly equiaxed. When TiB is used as the grain refiner, the resulting B content in the alloy may be up to 0.01 wt.%.

The aluminum alloys of the present disclosure may include Ti in some embodiments. However, high Ti contents may be detrimental to extrudability and may reduce extrusion rates and die life, so the concentration of Ti, if present, is limited to less than 0.05 wt. %, e.g., less than about 0.030, less than about 0.027, or less than about 0.024 weight percent. As indicated above, it may be desirable to add low levels of Ti to the extrusion alloy as a grain refiner during casting, either as Ti, or in combination with B as a TiB grain refiner, or in combination with C as a TiC grain refiner.

The aluminum alloy of the present disclosure may contain Ni in some embodiments. However, since Ni can reduce self-corrosion resistance, the Ni content is less than 0.01.

In the aluminum alloys of the present disclosure, Mg is optionally present but is kept relatively low, less than 0.05 wt.%, for the extrudability and brazeability of the alloy.
In some embodiments, the balance of the alloy includes aluminum and incidental impurities, hi some embodiments, each of the incidental impurities is present at a maximum of 0.05 (in some embodiments, 0.03), and the sum of the incidental impurities is less than 0.10.

The extruded and brazed products of the present disclosure include Al-Mn-Fe-Si dispersion particles. The Al-Mn-Fe-Si dispersion particles are sub-micron particles that affect the deformation behavior, recrystallization behavior, and resulting mechanical properties of products including the aluminum alloys of the present disclosure. In some embodiments, the dispersion particles allow for the retention of fine as-extruded grain structure in the outer wall of the tube after a typical cold sizing and brazing process, such as combining piping with fins and headers to make a brazed heat exchanger. Without being bound by theory, the retention of fine as-extruded grain structure in the outer wall of the shape after brazing contributes to corrosion resistance by providing a more tortuous corrosion path through the wall of the shape.

In one embodiment, the extruded and brazed product contains less than 15%, preferably less than 12%, and most preferably less than 10% coarse recrystallized grains across the width of the tube when subjected to harsh brazing and/or less than 5%, preferably less than 3%, and most preferably less than 1% recrystallized grains when subjected to standard brazing (e.g., standard controlled atmosphere (CAB) brazing, etc.). Percentage refers to the percentage of the tube outer wall that is made up of coarse recrystallized grains. In one embodiment, less than 15%, less than 14%, less than 13%, less than 12%, less than 11%, or less than 10% of the width of the extruded and brazed product is occupied by coarse recrystallized grains when subjected to harsh brazing and/or less than 5%, less than 4%, less than 3%, less than 2%, or less than 1% recrystallized when subjected to standard controlled atmosphere (CAB) brazing, which is commonly used in the manufacture of aluminum heat exchangers. Percentage refers to the percentage of the tube outer wall width that is made up of coarse recrystallized grains.

The extruded and brazed products may be provided in any shape or form. In some embodiments, the extruded and brazed products may be in the form of a tube or multiple tubes. In some specific embodiments, the extruded and brazed products may be or comprise micro multiport piping (MMP). When the extruded and brazed products are piping or tubes (such as MMPs), they may have a wall thickness of about 0.4 mm or less, about 0.3 mm or less, or about 0.2 mm or less.

The present disclosure also provides a method for producing an extruded and brazed product. The method includes processing an aluminum alloy of the present disclosure into an aluminum product. The processing step may include directly casting the aluminum alloy into an intermediate billet intended for extrusion.

In some embodiments, the method of the present disclosure first provides a billet comprising an aluminum alloy as described herein. The billet is then homogenized by at least one heat treatment, including a treatment temperature in the range of 540°C to 590°C for at least one soaking time in the range of 1 to 8 hours, to obtain a homogenized aluminum alloy billet. The billet is then extruded into a product, such as tubing. The product (tubing) is subsequently coiled, uncoiled, cold sized, assembled, and brazed as desired to obtain a brazed product (the tube forms part of a heat exchanger). The brazing process may include at least one brazing cycle.

In one embodiment of the method, the aluminum alloy of the present disclosure is cast into a billet prior to providing the billet. In one embodiment of the method, after homogenization and prior to brazing, the homogenized aluminum product is cooled, preferably at a cooling rate of 300°C/hour or less.

EXAMPLES Example I Effect of Mn and Fe on Recrystallization of Brazed Tubes Alloys A to E (detailed chemical compositions in Table 1) were direct chill (DC) cast as 101 mm billets. Alloy A represents the existing prior art and is the benchmark for comparison. The concentration of Mn in the experimental alloys was increased compared to alloy A, with alloys B and C containing 0.64 wt% Mn and alloys D and E containing 0.70 wt% Mn. The concentration of Fe was increased compared to alloy A only for alloys C and E, to 0.14 and 0.15 wt%, respectively.

Billets B-E were homogenized using four treatments, the first (TR1) at 550°C for 2 hours, the second (TR2) at 550°C for 6 hours, the third (TR3) at 560°C for 2 hours, and the fourth (TR4) at 560°C for 6 hours. Billet A was homogenized using TR1 and TR2 only. The billet was subsequently cooled at 300°C/hour. The cooled material was then extruded using a billet temperature of 480°C and an exit speed of 77 m/min into mini-microport (MMP) piping with an outer wall thickness of 0.35 mm. A length of piping was cold sized by rolling to a thickness reduction of 4% to replicate commercial tube sizing. Simulated brazing cycles of 605°C (cycle 1) and 625°C (cycle 2) for 2.5 minutes were then applied and the grain structure was assessed by macroetching of the outer flat surface of the tube and measuring the percentage of the tube width occupied by coarse recrystallized grains, where the term "coarse grains" refers to grains >200 microns wide that are on the extrusion surface or have a thickness that extends through the entire wall thickness. The results are shown in Table 2.

The degree of undesirable coarse recrystallized grains increased with increasing homogenization soak time/temperature and with increasing brazing temperature. Alloy A maintained a fine grain structure when homogenized for 2 hours/550°C and brazed at 605°C. However, extending the soak time at 550°C to 6 hours and brazing at 605°C resulted in significant recrystallization. Increasing the brazing temperature to 625°C showed excessive recrystallization at both soak times. Thus, variations in brazing temperature and homogenization soak time expected in commercial operations may result in excessive coarse recrystallized grains with Alloy A.

Under the experimental conditions tested, the acceptable targets for coarse grain formation are zero coarse grain formation after standard brazing at 605°C and <15% after more severe processing at 625°C. The latter corresponds to the formation of a single coarse grain at the tip (end) where the strain during sizing is more concentrated. In this example, alloy B performed slightly better than alloy A in terms of coarse grain formation. However, performance when brazed at 625°C was unacceptable at homogenization temperatures in the range of 550-560°C. Alloy C, along with alloy E, provided significantly better resistance to coarse grain formation, suggesting that increased Fe content is beneficial. Alloy D, which has a higher Mn content than alloy B but the same Fe content, exhibited unacceptable behavior at higher brazing temperatures, suggesting that increasing Mn content alone is insufficient to prevent coarse grain formation.

Example II: Effect of Si on the recrystallization of brazed tubes. Alloys A, F, G, and H (detailed chemical compositions in Table 3) were DC cast as 101 mm diameter billets. Alloy A represents the existing prior art and is the benchmark for comparison. Alloys F, G, and H had increased Si concentrations of 0.08, 0.14, and 0.19 wt.%, respectively.

The alloy was homogenized at 580°C for 6 hours to represent a long soak cycle at high temperature. The billet was subsequently cooled at 300°C/hour. The cooled material was then extruded using a billet temperature of 480°C and an exit speed of 77 m/min to form mini-microport (MMP) tubing with an outer wall thickness of 0.35 mm. Lengths of tubing were cold rolled to a thickness reduction of 4% to replicate commercial tube sizing and checked for oversizing as 10%. An extreme brazing cycle of 625°C for 2.5 minutes was then applied. Grain structure was assessed by macroetching of the tube plane and measuring the percentage of the tube width occupied by coarse recrystallized grains. The results are shown in Table 4.

As expected, alloy F, with a similar composition to alloy A but with increased Fe content, completely recrystallized to a coarse grain structure. However, alloy G, with increased Si from 0.08 to 0.14 wt%, provided significant control of post-braze grain size, and this trend continued in alloy H, with 0.19 wt% Si. Thus, by slightly increasing the Si content, post-braze grain structure can be controlled under severe processing conditions. Increasing the Si content from 0.08 to 0.19 reduces the melting point by 4°C, which may have some effect on extrudability. Therefore, further increases in Si beyond 0.19 wt% are not desirable.

EXAMPLE III Al-Mn-Fe-Si Disperse Modeling Without wishing to be bound by theory, it is believed that the mechanism for post-braze structure control and prevention of coarse grain recrystallization is due, at least in part, to grain boundary pinning by sub-micron alpha-Al-Mn-Fe-Si disperse particles that are assumed to form during homogenization. The pinning effect is proportional to the volume fraction/particle radius. The composition and homogenization cycle effects observed in these experiments were likely due to changes in these two parameters. Using a proprietary homogenization model that predicts disperse growth and solute diffusion across dendrite arms, it is possible to predict the effect of composition on disperse distribution. Figure 1 shows how disperse volume fraction varies with Fe and Si content during homogenization at 550°C in a 0.70 wt% Mn base alloy. At the base level of 0.08 wt% Si, increasing Fe from 0.10 to 0.15 wt% increased the volume fraction, but this began to decrease after 2-3 hours of soaking, implying that longer homogenization times may reduce the ability to prevent coarse recrystallized grain formation. Increasing the Si content from 0.08 to 0.13 wt% resulted in a lower initial dispersed grain volume fraction, but continued to increase with longer homogenization times, which may offset the effect of longer soak times and is possible under production conditions.

Example IV Corrosion Resistance Test Alloys A, B, C, D, E, F, G, and H were homogenized as described above and extruded into 30 x 1.4 mm strips using a billet temperature of 480°C and an exit speed of 75 m/min. Commercial alloy variants corresponding to AA3102 and established commercial long life alloys were also processed for comparison. The materials were quenched with water at the die exit. A simulated brazing cycle at 605°C for 5 minutes was applied to 100 mm coupons. These were degreased with alcohol and then four coupons per alloy were exposed to the SWAAT corrosion test (ASTM G85) for 20 days. The average pit depth was determined for each sample based on visually selecting the six deepest pits per coupon. Results after 20 days of exposure to accelerated corrosion tests are shown in Table 5. Small pit depth is desirable and is an indication of good resistance to pit corrosion in service. The established commercial long life alloy based on AA3012A performed best in SWAAT, but the experimental alloys B through E, including alloys C, E, G, and H of the present invention, all performed better than prior art alloys A and F, as well as the standard commercial alloy AA3102.

Example V Flow Stress Testing The extrudability or potential extrusion rate of Al-Mn type alloys is controlled by the alloy flow stress at high temperatures. Lower flow stress is an indication of potentially higher extrusion rates and reduced die wear. Billets of alloys C and E were homogenized in a 2 hour/550°C cycle followed by cooling at 250°C/hour, and alloys F, G, and H were homogenized in a 2 hour/580°C cycle followed by cooling at 250°C/hour. Samples of established commercial long life alloys were also processed using standard commercial practice. Cylindrical samples 10 mm diameter by 10 mm length were machined. Triplicate samples were subjected to hot compression testing using a Gleeble 3800 machine. Samples were heated to 450°C at 100°C/min, held for 5 minutes, and then compressively deformed to a strain of 0.8 at a strain rate of 1/sec. The recorded load was converted to true stress and the value at 0.7 strain was extracted as a measure of flow stress. The average flow stresses of alloys C, E, G, and H were 7-10% lower than existing established commercial long life alloys, which in all cases represents a significant improvement in extrusion performance.

Example VI: Grain structure of commercial scale brazed tubes The alloy compositions whose chemical details are given in Table 7 were direct chill (DC) cast into 203 mm diameter billets. The billets were then homogenized (4 hrs/550° C.) and cooled (215° C./hr).

The material was extruded in a commercial extrusion press into 0.3 mm wall microchannel tubing. The surface of the microchannel tubing was arc sprayed with zinc at the press exit before passing through a water quench. The tubing was wound on the press and then processed through an offline lengthening and sizing operation where the tube wall was reduced.

A laboratory furnace was used to apply simulated brazing thermal cycles of 605°C for 2 minutes, 605°C for 4 minutes, and an extreme cycle of 625°C for 4 minutes. Figures 4A and 4B show the corresponding surface grain structures revealed by Poulton macroetching. The "as-extruded tube" exhibited only fine grains. The post-braze grain structures after all three treatments were fine except for a narrow band of coarse recrystallized grains along one size of the tube. The band width corresponded to 6% of the tube width in all three cases.

Therefore, it will be understood that the examples described and illustrated above are intended to be illustrative only. The scope is indicated by the appended claims.

Claims (24)

1. An extruded and brazed product, including an extruded and brazed tube made of an aluminum alloy, comprising:
The aluminum alloy is in weight percent:
Mn 0.6 to 0.75,
Fe 0.11 to 0.16,
Si 0.10 to 0.19,
Cu < 0.01,
Zn < 0.05,
Ti < 0.05,
Optionally, a Ti-containing grain refiner;
Optionally, Ni <0.01, with the balance being aluminum and inevitable impurities;
It consists of:
Where:
The amount of Ti includes the Ti-containing grain refiner,
wherein less than 15% of the outer peripheral surface of said extruded and brazed tube perpendicular to the direction of extrusion comprises coarse recrystallized grains. The extruded and brazed product of claim 1, wherein each of the unavoidable impurities is present at a maximum of 0.05, and the sum of the unavoidable impurities is less than 0.10. The extruded and brazed product of claim 1 or 2, wherein the aluminum alloy contains less than 0.01 Ni. The extruded and brazed product of any one of claims 1 to 3, wherein the aluminum alloy contains less than 0.05% Mg. The extruded and brazed product of any one of claims 1 to 4, wherein the aluminum alloy contains less than 0.05% Cr. The extruded and brazed product of any one of claims 1 to 5, wherein the aluminum alloy contains 0.64 to 0.72 Mn. The extruded and brazed product of any one of claims 1 to 6, wherein the aluminum alloy contains 0.10 to 0.14 Si. The extruded and brazed product of any one of claims 1 to 7, wherein the aluminum alloy contains 0.12 to 0.16 Fe. The extruded and brazed product of any one of claims 1 to 8, wherein the aluminum alloy contains 0.011 to 0.024 Ti. The extruded and brazed product according to any one of claims 1 to 9, which is an extruded and brazed pipe. The extruded and brazed product of claim 10, wherein the extruded and brazed piping is or includes a micro-multi-port piping. 13. A method for producing the extruded and brazed product of claim 1 , comprising the steps of:
a) in weight percent:
Mn 0.6 to 0.75,
Fe 0.11 to 0.16,
Si 0.10 to 0.19,
Cu < 0.01,
Zn < 0.05,
Ti < 0.05,
Optionally, a Ti-containing grain refiner;
Optionally, Ni <0.01, with the balance being aluminum and inevitable impurities;
providing a billet made of an aluminum alloy comprising:
wherein the Ti amount includes the Ti-containing grain refiner,
b) homogenizing the billet by at least one heat treatment, the heat treatment comprising a treatment temperature in the range of 540°C to 590°C for at least one soaking time of 1 to 8 hours to obtain a homogenized aluminum alloy;
c) extruding the billet into a product to obtain an extruded product; and d) brazing the extruded product to obtain the extruded brazed product.
A method comprising: The method of claim 12, further comprising casting the aluminum alloy into the billet prior to providing the billet. The method of claim 12 or 13, further comprising cooling the billet after homogenization and before extrusion. The method according to any one of claims 12 to 14, wherein each of the inevitable impurities of the aluminum alloy is present at a maximum of 0.03, and the sum of the inevitable impurities is less than 0.10. The method according to any one of claims 12 to 15, wherein the aluminum alloy contains less than 0.01 Ni. The method according to any one of claims 12 to 16, wherein the aluminum alloy contains less than 0.05% Mg. The method according to any one of claims 12 to 17, wherein the aluminum alloy contains less than 0.05% Cr. The method of any one of claims 12 to 18, wherein the aluminum alloy contains 0.64 to 0.72 Mn. The method according to any one of claims 12 to 19, wherein the aluminum alloy contains 0.10 to 0.14 Si. The method of any one of claims 12 to 20, wherein the aluminum alloy contains 0.12 to 0.16 Fe. The method according to any one of claims 12 to 21, wherein the aluminum alloy contains 0.011 to 0.024 Ti. The method of any one of claims 12 to 22, wherein the extruded and brazed product is a pipe. The method of claim 23, wherein the piping is a micromultiport piping.

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