Zn添加对预时效态Al-Mg-Si-Cu合金自然时效和烘烤硬化性的影响

Effects of Zn Addition on the Natural Ageing Behavior and Bake Hardening Response of a Pre-Aged Al-Mg-Si-Cu Alloy

以含Zn和不含Zn的2种Al-Mg-Si-Cu合金为研究对象,研究了Zn添加(0.64%,质量分数)对预时效态Al-Mg-Si-Cu合金的自然时效行为和烘烤硬化响应的影响,并利用三维原子探针(3DAP)技术揭示了相关微观机理。结果表明,含Zn合金在80℃下预时效15 min后的自然时效过程中原子团簇的Zn含量增加,原子团簇的稳定性改变,与不含Zn合金相比,含Zn合金原子团簇生长得更快。含Zn和不含Zn合金在预时效后的自然时效过程中屈服强度增加,含Zn合金因为具有更小的原子团簇间距和更大的原子团簇剪切模量,其屈服强度始终高于不含Zn合金。预时效后自然时效不同时间后在170℃下进行30 min模拟烤漆处理,原子团簇向GP区和β"相的转变随着自然时效时间的延长而减弱,因此含Zn和不含Zn合金的烘烤屈服强度降低。Al基体中的Zn具有促进析出相转变的作用,因此含Zn合金的烘烤屈服强度始终高于不含Zn合金。

Al-Mg-Si(-Cu)alloys are widely used in automotive body panels because of their excellent combined performance of high strength-to-weight ratio,good formability and corrosion resistance.Zn additions to Al-Mg-Si(-Cu)alloys have been tested and shown to effectively affect the precipitation microstructure and enhance the age-hardening response.The present study investigates the natural ageing(NA)behavior and bake hardening response in the pre-aged Al-0.9 Mg-0.8 Si-0.2 Cu(mass fraction,%)and Al-0.9 Mg-0.8 Si-0.2 Cu-0.6 Zn(mass fraction,%)alloys.The results are compared to clarify the effect of Zn addition.During NA after pre-ageing at 80℃for 15 min(PA),cluster growth is the dominant process in the Zn-free and Zn-added alloys.Some Zn atoms are partitioned into the clusters under PA+NAcondition.Partitioning of Zn may change the stability of clusters,increasing the growth rate of clusters.The yield strength of the two alloys increases with the increasing NA time.The smaller cluster spacing and larger cluster shear modulus lead to the higher yield strength in the Zn-added alloy during NA after PA.The prolonged NA inhibits the transformation of clusters to GP zones andβ″phases during bake hardening(BH)treatment at 170℃for 30 min in the Zn-free and Zn-added alloys,resulting in the lower BH response.The Zn does not significantly partition into clusters or precipitates,and the majority of Zn remains in the Al matrix during BH treatment,prompting the transformation from solute clusters to GP zones andβ″phases.As a result,the yield strength of the Zn-added alloy after PA+NA+BH treatment is higher than that of the Zn-free alloy.