预应变和预时效对Al-Mg-Si合金烘烤硬化性能的影响

Effect of pre-straining and pre-ageing on bake hardening response of Al-Mg-Si alloy

采用硬度和单轴拉伸测试,结合差示扫描量热法(DSC),分析预时效、预应变和预应变后预时效3种预处理工艺对Al-Mg-Si合金自然时效的抑制及烘烤硬化性能的影响。结果表明:预时效能有效抑制合金的自然时效,提高烘烤硬化效果(BHR),但预时效时间为10 min时,烘烤前强度较高,并且烘烤后塑性降低;预时效前加入预应变不仅能进一步抑制合金的自然时效,且在烘烤强度明显增加的同时保持合金伸长率较高,其中合金经5%预应变及5 min预时效的烘烤硬化性能最好。预处理后合金的DSC曲线中原子团簇的溶解峰消失,且β″相析出峰提前,说明预处理可抑制合金在自然时效过程中原子团簇的形成,加速烘烤过程中β″强化相的析出从而抑制自然时效,增加烘烤效果。

The effects of pre-ageing, pre-straining and pre-straining in combination with pre-ageing on the suppressing of natural ageing and bake hardening response （BHR） of Al-Mg-Si alloys were investigated by means of hardness, tensile test and differential scanning calorimetry （DSC） analysis. The results show that pre-ageing can suppress natural ageing of the alloy and improve its BHR effectively. When pre-ageing time is 10 min, the strength of the alloy before baking is too high and the plasticity after baking decreases. Adding pre-straining before pre-ageing can suppress natural ageing further and retain the good elongation, while improves BHR obviously. The alloy after 5% pre-straining and 5 min pre-ageing sample has the best BHR. In DCS curves, the dissolution peak of clusters disappear, β＂precipitation peak shifts to lower temperature in pre-treated samples. It indicates that the pre-treatments suppress the formation of clusters during natural ageing of the alloy, and accelerate the precipitation of β＂ phase during baking, with the results of natural ageing suppressed and BHR enhanced.