预处理对汽车用Al-Mg-Si合金组织和晶间腐蚀行为的影响

Effect of pre-treatment on microstructure and intergranular corrosion behavior of Al-Mg-Si alloy for automobile

采用拉伸试验、晶间腐蚀试验、电化学测试、光学显微镜、透射电镜等方法手段研究了Al-Mg-Si合金在不同预处理条件下经烤漆处理后的微观组织与晶间腐蚀行为的演变规律。结果表明,随着预变形量的增加,试验合金晶界析出相的数量密度和尺寸相应地减小,而晶内析出物(β″相)的析出数量增加,尺寸减小,以致不同的预处理试验合金具有不同的综合性能。由预应变和预时效组成的预处理工艺有利于提高Al-Mg-Si合金的综合性能,其晶间腐蚀抗力和烘烤硬化性能都得到显著提高,这主要归因于合金在烤漆过程中不产生无析出区,形成的晶界析出物数量少而不连续,以及基体强化相β″相通过消耗大量溶质原子而充分地析出。

Evolution laws of microstructure and intergranular corrosion behavior of the Al-Mg-Si alloy after bake hardening under different pre-treatment conditions were studied by tensile test, intergranular corrosion test, electrochemical test, metallographic microscope and transmission electron microscope. The results show that with the increase of pre-straining amount, the quantity density and size of grain boundary precipitates of the tested alloy decrease correspondingly, while the intragranular precipitates(β″ phase) increase in precipitation quantity and decrease in size, so that the tested alloy pre-treated differently has different comprehensive properties. The pre-treatment process composed of pre-straining and pre-aging is very beneficial to improve the comprehensive properties of Al-Mg-Si alloy, the intergranular corrosion resistance and bake hardening property are significantly improved, which is mainly attributed to the fact that the tested alloy do not form precipitation-free zone during bake hardening process, the grain boundary precipitates are less and discontinuous, and the matrix strengthening phase(β″ phase) is fully precipitated by consuming a large number of solute atoms.