Thixoforming characteristics of thermo-mechanically treated AA 6061 alloy for suspension parts of electric vehicles
Thixoforming characteristics of thermo-mechanically treated AA 6061 alloy for suspension parts of electric vehicles
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DOI：
10.1016/s0924-0136(02)00818-x
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发表时间：
2002-12
影响因子：
6.3
通讯作者：
Sang-yong Lee;Se-I Oh
中科院分区：
文献类型：
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作者：
Sang-yong Lee;Se-I Oh
为制造低速电动汽车悬架转向节，对变形铝合金AA 6061合金进行了触变成形试验。作为起始材料的钢坯在随后的再加热过程中进行热机械处理，诱导出可触变成形的细小球状组织。在使用水平感应加热装置将段塞重新加热到工作温度（~ 645°C）后，通过将加热的段塞垂直注射到模腔中形成零件。除少数靠近浇口的表面区域偶尔存在未再结晶的大晶粒外，触变部位的大部分区域均可见发育良好的球状显微组织。但由于注射速度过快，导致了远、近浇口区域的液体偏析。用半固体特征流动行为解释其原因，并提出减少液体偏析的方法。为了评价AA 6061触变成形件的力学性能，采用一系列试样按其在零件中的切割位置仔细分类进行拉伸试验。拉伸试验结果表明，液体偏析对拉伸性能影响较大。特别是在T6条件下热处理时，拉伸性能的变化更为明显。这些结果可能是由于含有大量合金元素的液相偏析导致Mg、Si等合金元素偏析所致。因此，有必要减少液相偏析，以获得更均匀的拉伸性能。通过比较AA 6061触变成形件与铸造级A357合金触变成形件的拉伸性能，发现AA 6061触变成形件在成形状态和T6状态下，尽管强度水平略低于A357件，但其延展性要好得多。研究结果表明，变形铝合金AA 6061具有合理的触变成形性能和力学性能，适用于转向节等实物零件的触变成形。
Thixoforming trials of AA 6061 alloy, which is a wrought aluminum alloy, were undertaken to manufacture the steering knuckles designed for suspension parts of low speed electric vehicles. The billets used as a starting material were thermo-mechanically treated to induce thixoformable fine globular microstructures during subsequent reheating process. After a slug was reheated up to the working temperature (∼645°C) using the horizontal induction heating device, the part was formed by vertical injection of a heated slug into the die cavity. The well-developed globular microstructures could be observed in most sections of the thixoformed parts except few surface regions close to gate where occasional unrecrystallized large grains are present. However, liquid segregation between near and far gate region could not be avoided, which was probably resulted from high injection speed. The reason for that will be explained using semi-solid characteristic flow behaviors and the method to reduce liquid segregation will be suggested. In order to evaluate the mechanical properties of AA 6061 thixoformed parts, a series of test specimens carefully classified by their cutting location in a part were used for tensile test. From tensile test results, it could be revealed that tensile properties were strongly affected by liquid segregation. Especially, variation of tensile properties was more dominant when the part was heat treated by T6 condition. These results may be attributed to the segregation of alloying elements such as Mg and Si caused by the segregation of liquid phase involving much alloying element. Therefore, it is necessary to reduce liquid phase segregation in order to obtain more uniform tensile properties. By comparing tensile properties of AA 6061 thixoformed parts to those of previously thixoformed parts made from cast grade A357 alloy, it was found that AA 6061 parts showed far better ductility, even though strength level is slightly lower, than A357 parts at both as-formed and T6 condition. In this study, it was confirmed that wrought aluminum alloy, AA 6061 has the reasonable thixoformability and mechanical properties for thixoforming of real parts such as steering knuckles.