拉伸变形对AA6016铝合金汽车外板再结晶组织及性能的影响

为优化冲压成形工艺,研究了不同拉伸形变量对T4P态AA6016冷轧薄板再结晶、析出行为、烘烤硬化性及断裂方式的影响规律.采用与气垫炉生产线类似的新型热处理设备,对合金进行固溶处理,预时效后室温停放,获得T4P态合金.以单向拉伸模拟板材局部冲压成形过程,采用金相显微镜、扫描电镜和透射电镜,对合金再结晶组织、拉伸断口以及位错进行观察,并结合DSC测定和拉伸性能测定,对合金析出行为及力学性能表征.结果表明:随拉伸形变量增加,局部晶粒有被拉长的趋势;形变可抑制GP区溶解,并促进强化相析出;烘烤硬化性随形变增加而减弱;形变较小时,烘烤前后断裂方式均为塑性断裂,而形变较大时,烘烤前合金更加趋向于解理断裂,烘烤后解理断裂趋势减弱.

Influence of tensile deformation on recrystallization and mechanical properties of AA6016 aluminium alloy used for automotive body outer sheet

In order to optimize stamping process, the effect of tensile deformation on recrystallization, precipitation behavior, bake hardenability and fracture mechanisms of a cold-rolled AA6016 sheet with T4P state were investigated. The alloy was solution heat treated in new heating treatment equipment, similar to air-cushion furnace production line, and then pre-aged immediately. After that the sheet was placed at room temperature in order to achieve T4P state. The local stamping process was simulated by uniaxial tensile. Recrystallization, fracture and dislocations were observed by optical microscopy, scanning electron microscopy and transmission electron microscopy respectively. Combined with differential scanning calorimetry (DSC) and tensile tests, precipitation behavior and mechanical property were characterized. The results indicated that local grains were elongated with the increasing of the deformation. GP zones were suppressed, and strengthening phase precipitation was promoted by deformation. Bake hardenability decreased with the increasing of the deformation. The fracture mechanisms were plastic fracture before and after bake hardening with small deformation. While the alloy tended to cleavage fracture before bake hardening, and the trend of cleavage fracture weakened after bake hardening with large deformation.