JP4871190B2 - Aluminum clad rolling method - Google Patents

Description

  The present invention relates to a method for producing an aluminum alloy clad material such as an aluminum alloy brazing sheet used in an automobile heat exchanger or the like. Specifically, the interface does not peel in the rolling process, and the production efficiency is improved. It relates to a rolling method.

  In the field of heat exchangers such as automobiles, brazing sheets made of aluminum alloy are used from the viewpoint of environmental problems and weight reduction that do not require the use of lead for brazing like conventional copper brazing sheets. It has become. This aluminum alloy brazing sheet is usually a sacrificial anode material made of a general Al-Zn alloy 3003 alloy as a core material and made of an alloy containing Zn such as an Al-Mn alloy on the water contact side. However, a three-layer structure using an Al—Si alloy or the like as a brazing material on the surface opposite to the water contact side is known. This three-layered brazing sheet is generally produced by heating a sacrificial anode material and a brazing material on both sides of the core material, followed by hot rolling and further cold rolling.

Conventionally, in the hot rolling, when the amount of reduction per pass is increased in order to press the sacrificial anode material and the brazing material to the core material, respectively, at the clad (laminated) interface (hereinafter referred to as the interface). Peeling occurs due to shear deformation. For this reason, in order to prevent peeling while performing crimping, a pass schedule that repeats light reduction is usually employed, particularly on the front side of the rolling process. Moreover, in patent document 1, since light reduction is effective for the crimping | compression-bonding problem, the reduction rate in 60% or more of plate thickness before the rolling start is 1.0% or more and 5.0% or less, A manufacturing method in which light pressure is reduced as compared with the latter stage side is disclosed.
JP-A-9-184038

  However, as described above, it is possible to promote the pressure bonding of the both surface layer materials to the core material and to prevent peeling by repeating the light reduction particularly at the front side of the rolling process, but repeating the light reduction is not possible. Therefore, a large number of passes are required until the plate thickness is reduced to the required plate thickness, resulting in a significant reduction in productivity. For this reason, it is conceivable to improve productivity by first determining the limit reduction amount at which peeling does not occur experimentally and performing rolling within the range of the reduction amount. However, in such a method for determining the pass schedule, for example, in the heating furnace, the material (raw material) temperature rises as the heating time becomes longer, or conversely, the material (rolling) becomes longer as the waiting time outside the furnace becomes longer. Material) Under the influence of operational troubles such as a decrease in temperature, the temperature of the plate material (raw material or rolled material) to be actually rolled changes (varies). Since such a change in material temperature affects the peeling behavior of the cladding interface, this experimentally determined pass schedule causes peeling of the cladding interface in consideration of the fluctuation range of such material temperature. There will be no choice but to set the amount of reduction on the safe side. When such a pass schedule (rolling amount) is set, the safety-side rolling amount setting is performed assuming the above operational troubles even though high pressure can be achieved without causing separation of the cladding interface. This causes the problem of reduced productivity.

  As described above, since the aluminum clad material is manufactured by hot crimping, if the high pressure is applied to the non-crimped material, the crimping interface peels off due to the warp on the exit side of the rolling mill, and the clad material is removed. There is a problem that it cannot be manufactured, and even if it is not an uncompressed material, even if it is welded around the interface of the clad material or even if the crimping strength is insufficient at the initial (stage) pass, the material is subjected to high pressure For the same reason as in the case of the non-bonded material, the cladding interface peels off. For this reason, high reduction cannot be performed until the pressure bonding strength at the clad interface becomes sufficient, and rolling under light reduction with low productivity has to be continued.

  Therefore, the problem of the present invention is that when an aluminum alloy clad material is manufactured by hot rolling, even if the temperature of the rolled material fluctuates due to operational troubles, it is possible to prevent the pressure bonding at the layer interface and prevent peeling. It is an object of the present invention to provide a method for determining a pass schedule of an aluminum alloy clad material that can easily calculate an appropriate reduction amount (reduction rate) in each pass and contribute to an improvement in productivity.

  In order to solve the above problems, the present invention employs the following configuration.

  The method of rolling an aluminum clad material according to claim 1 is a method of rolling an aluminum clad material in which aluminum or aluminum alloy plate materials are laminated and the interface is joined by hot rolling, and an index of interfacial bonding strength that does not cause peeling. The critical maximum shear stress τ (limit) is calculated in advance, the surface temperature of the rolled material is measured for each hot rolling pass, and the calculated internal temperature of the rolled material is taken into account based on the measured surface temperature. The maximum shear stress τ acting on the interface is predicted by numerical analysis, and the rolling reduction rate or rolling amount for each pass is determined so that the predicted maximum shear stress τ does not exceed the critical maximum shear stress τ (limit). It is characterized by that.

  As a result of earnest investigation of the phenomenon in which peeling occurs at the clad interface under the above-described strong pressure, the present inventor has found that the shear stress acting on the clad interface on the rolling mill exit side is the cause. Moreover, among these shear stresses, it was found that the maximum value of the shear stress, that is, the maximum shear stress (τmax) when the stress is acting in the direction of peeling the interface in the direction perpendicular to the interface, is important. Since this maximum shear stress increases as the rolling reduction increases, this is the reason why a large rolling amount cannot be obtained in the initial stage of rolling, that is, strong rolling cannot be performed. The maximum shear stress at this time depends on the deformation resistance of the side material of the clad material, and increases as the deformation resistance increases. Therefore, when the changed plate (rolled material) temperature is lowered due to operational troubles as described above and temperature changes in the heating furnace, deformation resistance is increased and interfacial delamination is likely to occur, and conversely, the plate temperature is increased. It has been found that the deformation resistance is reduced and interfacial peeling is less likely to occur. Thus, by evaluating the maximum shear stress τmax at the clad interface based on the temperature of the rolled material, the temperature dependence of the limit reduction amount (ΔH (limit)) at which no interfacial delamination occurs is clarified. In addition, since the aluminum clad material has good thermal conductivity for both the side material and the core material, the aluminum clad material is in a substantially uniform temperature state in the heating furnace. By measuring the surface temperature, the thickness direction of the clad material Can be easily estimated.

  Utilizing the above knowledge, if the surface temperature of the rolled material is known before the start of each rolling pass, the center temperature is the furnace temperature at the initial stage of rolling, and thus the internal temperature distribution of the rolled material can be known. Considering this internal temperature distribution, comparing the maximum shear stress τmax obtained by numerical analysis and the critical maximum shear stress τ (limit) where no interfacial delamination occurs experimentally, the maximum shear stress τmax is The amount of rolling that does not exceed this critical maximum shear stress τ (limit) can be determined. That is, the reduction amount (reduction ratio) in each pass is increased in a range where the maximum shear stress τmax at the interface in each pass is equal to or less than the critical maximum shear stress τmax corresponding to the interface bond strength of the limit at which separation does not occur. It is possible to take. The rolling amount (rolling rate) determined in this way is the limit (upper limit) rolling amount (rolling rate) at which interfacial delamination does not occur at all times, so eliminate the light rolling path with a smaller rolling reduction than necessary. This contributes to a significant improvement in rolling efficiency (productivity). Also, when rolling clad materials having different materials and number of layers, the rolling pass schedule can be determined efficiently with a small number of trial rollings. As described above, the critical maximum shear stress τ (limit) means the maximum shear stress that does not lead to interface delamination in the area where tensile stress is applied to the interface, and is based on analysis based on actual rolling data. Can be calculated in advance as a function of cumulative strain. Strictly defined, this cumulative strain is the true strain accumulated at the cladding interface. For convenience, the total strain εt from the first pass, that is, the entire clad material (laminated material) is one sheet as the cumulative strain. The cumulative reduction ratio from the first pass when viewed as a plate material can be used. The maximum shear stress τmax is normally the shear stress acting on the exit side of each pass.

  In this invention, in determining the pass schedule of aluminum clad rolling in which aluminum or aluminum alloy plate materials are stacked and the interfaces are joined by hot rolling, the surface temperature of the plate material (rolled material) is measured before the start of each rolling pass. , The maximum shear stress (τmax) obtained by numerical analysis in consideration of the internal temperature distribution of the rolled material, and the critical maximum shear stress τ (limit ) And the maximum shear stress (τmax) does not exceed the critical maximum shear stress τ (limit), that is, rolling is performed at a limit reduction amount at which no interfacial separation occurs. Even if the temperature of the rolled material fluctuates due to fluctuation or the like, it is possible to perform rolling with a critical reduction amount that does not always cause interface separation. By simply comparing the maximum shear stress (τmax) determined by numerical analysis with the experimentally determined critical maximum shear stress τ (limit), the limit rolling amount at which no interfacial debonding occurs is determined and the pass schedule is determined. Compared to the case of deciding, it can cope with operational fluctuations and can always roll with the critical reduction amount from the initial stage of rolling, so it can realize a pass schedule with higher production efficiency and increase productivity during clad rolling. It can be significantly improved.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 and 4.

  As shown in FIG. 1, it is necessary to first measure the surface temperature of the rolled material before the start of each rolling pass, taking as an example a three-layer clad material in which both the side material and the core material are made of an aluminum alloy. The gender will be specifically described. FIG. 2 shows the maximum shear stress (τmax) acting on the clad interface by rolling, using the temperature distribution in the plate thickness direction near the surface of the clad material that has been reduced by air cooling (after extraction from the heating furnace). . From this figure, since the temperature distribution in the plate thickness direction of the clad material shifts to the low temperature side as the surface temperature decreases, the same rolling reduction ratio Rs (Rs = rolling amount / shown in FIG. 1) The maximum shear stress (τmax) acting on the cladding interface increases even with the total thickness. In addition, since the plate | board thickness reduction | decrease by rolling substantially arises only by the side materials 1a and 1b, the rolling reduction rate was evaluated by the side material rolling reduction rate Rs. When this maximum shear stress (τmax) exceeds the peeling limit stress at the cladding interface, interface peeling occurs. Therefore, as described above, the reduction rate (the amount of reduction) is adjusted, and this peeling limit stress, that is, the critical maximum shear stress τ (limit) It is necessary to set the following path schedule. In addition, if an example of the thickness of an aluminum clad material is given, the side materials 1a and 1b will be about 60-120 mm, and the core 1c will be about 600 mm.

  Since it is difficult to theoretically determine the critical maximum shear stress τ (limit), it is experimentally, that is, based on actual machine experiments or rolling results data, a rolling reduction at which interface peeling does not occur, a finite element method, etc. The critical maximum shear stress τ (limit) can be obtained by comparing the maximum shear stress (τmax) acting on the clad interface calculated using the analysis means. At that time, in the present invention (this embodiment), the maximum shear stress acting on the clad interface in consideration of the temperature distribution in the plate thickness direction of the clad material by measuring the surface temperature of the rolled material (clad material). (Τmax) is calculated to obtain the critical maximum shear stress τ (limit). Specifically, the temperature distribution in the plate thickness direction of the clad material is taken into consideration as follows. That is, various air cooling times are assumed with respect to the initial center temperature T0 (T0: heating temperature) of the clad material, and the surface temperature Ts, the center temperature Tc, and the temperature in the plate thickness direction that change in accordance with the air cooling time. A distribution T (h) is obtained. Corresponding to these temperature distributions T (h), Ts, and Tc, a deformation resistance distribution in the plate thickness direction of the clad material is given. In the clad material, since the material is different between the side material and the core material, a deformation resistance distribution occurs due to a material factor in addition to the temperature distribution. For the clad material having such a deformation resistance distribution, the shear stress τ acting on the clad interface is obtained by numerical analysis using the analysis means such as the finite element method, and the shear stress τ is perpendicular to the interface. The critical maximum shear stress τ (limit) can be obtained by comparing the maximum shear stress (τmax) when the stress is acting in the direction of peeling the interface in the direction with the reduction ratio at which no interface peeling occurs. . The maximum shear stress (τmax) is tabulated for each cladding material in the form of a function having the surface temperature Ts, the center temperature Tc, and the rolling reduction Re as variables, or for these variables Ts, Tc, and Re. In advance. Thus, by storing the maximum shear stress (τmax) in the form of a function or a table value in advance, even when the surface temperature of the rolled material changes, the surface temperature Ts is measured, and the plate is obtained online. The temperature distribution T (h) in the thickness direction is calculated to determine the center temperature Tc, and the maximum shear stress (τmax) acting on the cladding interface can be quickly determined. This maximum shear stress (τmax) and the critical maximum shear By comparing with the stress τ (limit), the presence or absence of interface peeling can be determined. And the maximum rolling stress (τmax) does not exceed the critical maximum shearing stress τ (limit), that is, the critical rolling reduction at which no interfacial separation occurs can be calculated quickly.

  FIG. 3 shows an apparatus configuration used in the aluminum clad material rolling method of the embodiment. In the process computer 2 for controlling the rolling of the clad material, the output information from the thermometer for measuring the heating temperature of the clad material in the heating furnace 3 and the temperature arranged on the entry side of the rolling mill 4 Output information from a total of 5 is fetched. The storage device 2a of the process computer 2 stores a database (DB) storing function forms or table values for calculating the maximum shear stress (τmax) online. The storage device 2b stores a database (DB) storing the critical shear stress τ (limit) for each material of the clad material. Further, another storage device (not shown) of the process computer 2 stores a temperature analysis program for calculating a temperature distribution in the plate thickness direction from an actual measurement value of the surface temperature Ts of the rolled material (clad material). Based on the measured value of the temperature Ts, an appropriate reduction rate (appropriate reduction amount), that is, a critical reduction rate (amount of reduction) at which no interfacial peeling occurs is quickly calculated online so that the roll gap of the rolling mill 4 is set. It has become. As a function form of the maximum shear stress (τmax), a function τmax = F (Tc, Ts, Re) composed of a polynomial having the surface temperature Ts, the center temperature Tc, and the rolling reduction Re as variables is used for each cladding material. The function form can be determined by regression analysis of data obtained in actual machine experiments and rolling performance data. Similarly, the table of the maximum shear stress (τmax) is obtained from the data obtained in the actual machine experiment and the rolling record data for each clad material, the clad material surface temperature Ts, the center temperature Tc, and the rolling reduction Re (or the rolling amount ΔH). Can be created as index parameters.

  FIG. 4 shows a flow for calculating inside the process computer 1 the limit rolling reduction Re (max) at which the interface peeling does not occur. In this calculation flow, the symbol i indicates a rolling pass number. That is, i = 1 indicates an initial (first) path, and i = n indicates a final path (n: the number of paths). From the material of the clad material, the database DB shown in FIG. 3 is used to determine a function or a table to be referred to and the critical maximum shear stress τ (limit) of the maximum shear stress τmax at the clad interface (S10, S20). . Next, the heating temperature T0 of the clad material and the rolling temperature Ts before the first pass are measured with a thermometer, and this temperature information is taken into the process computer, respectively (S30, S40). In the first pass, the center temperature Tc of the clad material is set to the heating temperature T0 (S50). Then, an initial (first pass) reduction ratio Re (1) is set (S60). Hereinafter, a case where the maximum shear stress τmax is obtained by a function, for example, a function F (Tc, Ts, Re (i)) will be described. The same applies when obtaining with reference to the table.

  First, a procedure for determining an appropriate rolling reduction that does not cause interface peeling in the first pass, that is, the maximum (limit) rolling reduction Re (1) max will be described. From the set initial rolling reduction Re (1) and the measured cladding surface temperatures Ts and Tc, the maximum shear stress τmax is calculated by the function F (Tc, Ts, Re (1)) (S70). If this maximum shear stress τmax <critical maximum shear stress τ (limit), the set reduction ratio Re (1) can still be increased, so τmax is set to F (Tc, Ts, Re (1) + δr). Recalculate (S80). At this time, δr is an arbitrary increase in rolling reduction. If F (Tc, Ts, Re (1) + δr)> τ (limit), the set rolling reduction Re (1) becomes the maximum (limit) rolling reduction Re (1) max that does not cause interface peeling (S110). ) The roll gap of the rolling mill is set so that this maximum rolling reduction is obtained. On the other hand, even if the reduction rate is increased by δr from the set value Re (1), if F (Tc, Ts, Re (1) + δr) <τ (limit), the reduction rate can be further increased. Therefore, the calculation of the maximum shear stress τmax is repeated with Re (1) = Re (1) + 2 × δr (S90). On the other hand, if F (Tc, Ts, Re (1) + δr)> τ (limit) in S70, the set rolling reduction ratio Re (1) is too large, so Re (1) = Re (1) −2. As xδr (S100), the maximum shear stress τmax is recalculated (S70). For the second and subsequent passes (i = 2 to n), based on the measured surface temperature Ts (S40) of the clad material, the temperature distribution T (h) and the center temperature Tc in the plate thickness direction of the clad material are determined by temperature analysis. Obtaining (S130), as in the case of the first pass, the calculated maximum shear stress τmax and the critical maximum shear stress τ (limit) are compared to determine the maximum (limit) rolling reduction Re (i). Thus, based on the measured value of the surface temperature Ts of the clad material before the start of rolling in each pass, the maximum (limit) rolling reduction at which interface peeling does not occur can be always obtained. Note that the amount of reduction may be obtained instead of the reduction rate.

It is explanatory drawing which shows typically an example of the laminated structure of a clad material. It is explanatory drawing which shows the relationship between the rolling reduction of a clad material, and the maximum shear stress which acts on an interface. It is explanatory drawing which shows the apparatus structure of embodiment typically. It is explanatory drawing of the calculation flow which determines the maximum (limit) rolling reduction of embodiment.

Explanation of symbols

1: Clad material 1a, 1b: Side material slab 1c: Core material
2: Process computer 2a, 2b: Storage device 3: Heating furnace 4: Rolling mill 5: Thermometer

Claims (1)

  A method of rolling aluminum clad material in which aluminum or aluminum alloy sheets are laminated and the interface is joined by hot rolling, and the critical maximum shear stress τ (limit), which is an index of interfacial bond strength that does not cause separation, is calculated in advance. Then, the surface temperature of the rolled material is measured for each hot rolling pass, and the maximum shear stress τ acting on the interface is numerically analyzed in consideration of the internal temperature of the rolled material calculated based on the measured surface temperature. A rolling method for an aluminum clad material, characterized in that the rolling reduction rate or rolling amount for each pass is determined so that the predicted maximum shearing stress τ does not exceed the critical maximum shearing stress τ (limit).

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