JP4277698B2 - Aluminum alloy sheet for body sheets with excellent laser weldability - Google Patents

Description

  The present invention relates to an aluminum alloy plate for a body sheet that is mounted, for example, as an inner plate or an outer plate of a vehicle. When assembling a plate material into a vehicle body shape after press molding, or before pressing, plates having different plate thicknesses are welded. The present invention relates to an aluminum alloy plate for a body sheet that is excellent in laser weldability when producing a tailored blank material.

Steel sheets are generally used for body sheets such as inner and outer plates mounted on vehicles. Recently, aluminum alloy plates with excellent light weight have been proposed for the purpose of improving fuel economy by reducing the weight of the vehicle body. Has been.
As an aluminum alloy plate used for such applications, for example, in Japanese Patent Laid-Open No. 9-137243, Mg2 as an aluminum alloy plate excellent in yield strength after baking and baking, normal temperature aging resistance, corrosion resistance, and press formability. Contains 0 to 3.0 wt%, Cu 0.30 to 0.60 wt%, Si 0.08 to 0.15 wt%, Ti 0.005 to 0.15 wt%, B0.0002 to 0.05 wt%, and further Mn0.05 to 0.30 wt%, An aluminum alloy sheet excellent in bendability after press forming containing one or more of Cr 0.05 to 0.10 wt% and Zr 0.05 to 0.10 wt% is disclosed.
JP-A-9-137243

In order to use an aluminum alloy plate as a body seat, each part is press-molded along the shape of the vehicle, and the resulting molded parts are fixed to a frame that has been assembled into a vehicle outer shape in advance. It is assumed that a body is formed.
After the vehicle body is formed, the body sheet surface is painted, and the paint is baked to make up the makeup.

In order to fix the part molded body to the frame, arc welding such as MIG welding is advantageous in that continuous automatic control is possible and the cooling rate after welding is slow, and as a result, there is little risk of occurrence of cracks in the welded part. This arc welding has the disadvantages that it has a large weld pool area and a wide range of influence of softening on the plate.
In addition, this arc welding has a low welding speed, and therefore the productivity is low.

  In order to eliminate these drawbacks, laser welding and laser / arc hybrid welding with high welding speed and good productivity have been proposed. However, in the case of the current 5000 series aluminum plate, there is a problem that cracks are likely to occur in the welded part in the case of laser welding or laser-arc hybrid welding.

  An object of the present invention is to propose an aluminum alloy plate for a body sheet of a vehicle that is less likely to cause cracks at a welded part even by laser welding.

 That is, the present invention is Mg: 2 to 6 wt%, Mn: 0.05 to 0.5 wt%, more than Zr0.12 and less than 0.20 wt%, Ti: 0.05 to 0.25 wt%, B: 0.0010 to 0.20 wt%, Zr + Ti : An aluminum alloy plate for vehicle body sheets having excellent laser weldability, comprising 0.20 wt% or more, comprising the balance Al and inevitable impurities, and having a plate thickness of 2 mm or less. Further, it is an aluminum alloy plate for body sheets that can further contain Cu: 0.10 and 0.5 wt% or less.

  The aluminum alloy plate for body sheets of the present invention is excellent in drawability by containing Mg. In addition, the inclusion of Zr, Ti and B has an effect that there is no possibility of cracking at the welded part even when laser welding is performed. Further, by further containing Cu, high strength can be imparted (baking curability) by baking coating treatment.

Next, each component will be described.
<Mg: 2-6wt%>
Mg is an element that imparts strength to the alloy plate and improves drawability. If the Mg content is less than the lower limit, the effect is small, and if it exceeds the upper limit, the SCC resistance is poor. Preferably, Mg is 2.5 to 4.5 wt%.

<Mn: 0.05-0.5wt%>
Mn is added for recrystallized grain refinement of the aluminum alloy plate, and if it is less than the lower limit, the effect is insufficient, and if it exceeds the upper limit, a coarse crystallized product is formed and the formability is poor.

<Zr: more than 0.12 and less than 0.20 wt%, Ti: 0.05 to 0.25 wt%, B: 0.0010 to 0.20 wt%, Zr + Ti: 0.20 wt% or more>
By containing Zr, Ti and B at the same time, they are elements for preventing the occurrence of cracks in the welded part of laser welding. If the content of Zr, Ti, and B, and Zr + Ti is less than the lower limit, the effect is small, and if Zr, Ti, and B exceed the upper limit, coarse intermetallic compounds are crystallized during casting, and formability is poor. Preferably, Zr: 0.15 wt% or more, Ti: 0.10 wt% or more, B: 0.005 wt% or more, Zr + Ti: 0.25 wt% or more, Zr + Ti: 0.35 wt% or less.

<Cu: over 0.10, 0.5: wt% or less>
Cu is an element for imparting higher strength in the paint baking process by further containing it in the aluminum alloy having the above composition. When the Cu content is lower than the lower limit, the effect is small, and when the Cu content exceeds the upper limit, the hemming property is inferior.

<Inevitable impurities>
Aluminum alloy is a process of melting using metal, return material, master alloy, metal elements, etc., and various elements other than the target element are mixed, but as long as the mixed amount of mixed elements is low, The effects of the invention are not impaired, and therefore, such mixed elements are treated as inevitable impurities in the present invention. That is, Si and Fe: 0.6% or less, Cu: 0.10 wt% or less, Cr: 0.3wt% or less, Ni: 0.1wt% or less, Zn: 0.5wt% or less, Ga: 0.1wt% or less, V: 0.1wt% The content of each of the following and other elements of 0.1 wt% or less does not impair the effect of the present invention, and such mixed elements are inevitable impurities in the present invention.

<Thickness 2mm or less>
The thickness of the aluminum alloy plate is an important factor for the occurrence of cracks in the welded part in laser welding. If the plate is thicker than 2 mm, the cooling rate after laser welding is slow and cracking is mitigated. Therefore, the device of the present invention is not necessary. Therefore, in the present invention, the occurrence of cracks is reliably prevented by adopting the above-described composition within a range where the thickness is small and the thickness is 2 mm or less and cracks are likely to occur. The plate thickness is preferably 1.5 mm or less, more preferably 1.0 mm or less, and further effects can be exhibited. The lower limit is about 0.5 mm from the viewpoint of use.

An embodiment of the present invention will be described.
Melting, casting, and rolling of the alloy plate of the present invention are not particularly limited and are produced by a conventional method. That is, the casting method may be a DC method for casting an ingot having a thickness of 500 to 600 mm, or a CC method for casting with a thickness of 10 mm or less. The aluminum alloy plate rolled to a thickness of 2 mm or less, preferably 0.5 to 1.0 mm, is press-formed on each part of the vehicle roof, side panel, bonnet, trunk, etc., and the parts are combined and laser welded, Alternatively, the parts are joined together with a vehicle frame as a support core and laser welded. Alternatively, plates having different thicknesses can be laser-welded to form a so-called tailored blank, and the tailored blank can be press-molded into a required shape of the vehicle. Alternatively, laser-arc hybrid welding may be performed in which laser welding is preceded and arc welding is followed, and arc welding is performed on the beads of the preceding laser welding.

As this laser welding, known carbon dioxide laser welding and YAG laser welding can be used. For laser welding, any method such as pulse welding or continuous welding may be used. For example, in the atmosphere, welding is performed using He, Ar, N, or a mixed gas thereof as an assist gas. To do.
Welding conditions are not uniform depending on the thickness of the plate, but welding is performed by appropriately determining output, defocusing distance, welding speed, and the like. For example, welding can be performed with appropriate consideration of welding speed 1 to 4 meters / min, laser output 0.5 to 5 KW, condensing diameter, frequency, atmospheric gas, etc., but these conditions do not limit the present invention. .

  The welded and integrated vehicle body is painted and baked. This baking treatment is 160-200 ° C. x 30 minutes to 1 hour in total to enhance the curing.

Aluminum alloy melts of various compositions were melted, cast and rolled into cold-rolled sheets having a thickness of 4.0 mm and 1.0 mm. Zr was added using an Al—Zr master alloy, and Ti and B were Ti metal or Al—Ti or Al—Ti—B master alloy. Table 1 shows the composition of the cold rolled sheet.
A cold-rolled sheet having a thickness of 4.0 mm was subjected to batch annealing (330 ° C. × 2 hours). In addition, 1.0 mm cold-rolled sheets were annealed (450 ° C. × 10 seconds) with an electromagnetic induction heating device, and water-quenched.
The following measurements were performed using these plates. The results are shown in Table 2.

<Weldability>
The obtained plates were butt-matched with a common material, YAG laser welded under the following conditions, and the presence or absence of cracks was confirmed with a 40 × optical microscope. No crack is indicated by ○, and crack is indicated by ×.
[YAG laser welding]
Welding speed 1.5m / min,
Laser power 2Kw
Frequency 100Hz,
Atmospheric gas Ar

  From the results of Table 2, the present invention example (sample numbers 1, 2, 3, 4, 5) using the present invention alloy (alloy code ABCD) with a high content of B, Zr, Ti and Zr + Ti is It can be seen that a thin aluminum alloy plate is excellent in laser weldability without cracking even when laser welding with a high welding speed is employed.

  On the other hand, the comparative example (sample No. 6) using the comparative alloy (alloy code E) with a small amount of Zr and B does not generate weld cracks because the plate thickness is thick, but in the thin aluminum alloy plate, B, Zr In comparative examples using comparative alloys (alloy codes E, F, G) with low Ti or Zr + Ti, the welding speed is fast (sample numbers 7, 8, 9) or slow (sample numbers 10, 11, 12) However, it can be seen that cracks occur in YAG laser welding.

A 1 mm thick annealed and water-quenched aluminum alloy sheet (alloy codes B and D) produced in Example 1 was subjected to heat treatment at 190 ° C for 30 minutes after applying 5% pre-strain assuming press working. The yield strength of the aluminum alloy sheet was measured.
The results are shown in Table 3.

  From the results of Table 3, it can be seen that the present invention alloy containing Cu is further excellent in bake hardenability in addition to the above-described effects.

  Since the aluminum alloy plate according to the present invention does not generate cracks in the welded part by laser welding even if the plate thickness is thin, there is a possibility that it can be effectively used as a vehicle body sheet with good productivity.

Claims (2)

Mg: 2 to 6 wt%, Mn: 0.05 to 0.5 wt%, Zr: more than 0.12 and less than 0.20 wt%, Ti: 0.05 to 0.25 wt%, B: 0.0010 to 0.20 wt%, Zr + Ti: 0.20 wt% or more An aluminum alloy plate for a body sheet excellent in laser weldability, comprising a balance Al and inevitable impurities and having a plate thickness of 2 mm or less. The aluminum alloy plate for body sheets having excellent laser weldability according to claim 1, further comprising Cu0.10 exceeding 0.5wt%.