Cu含量对铝硅合金热暴露后显微组织和拉伸性能的影响

Effect of Cu Content on the Microstructure and Tensile Properties of Al-Si Alloy after Thermal Exposure

针对于我国多种柴油机缸盖和机体所使用的ZL702A合金在高温工作过程中经常出现过早失效的情况,对Al-7Si-xCu-0.3Mg-0.3Zn(xw(cu)=1.5,2.5,3.5%)合金分别在200℃和250℃进行了0～1 000 h恒温处理试验(热暴露),测试了合金热暴露后其室温拉伸性能随时间的变化规律,采用光学金相显微镜、透射电子显微镜观察了合金显微组织的变化,综合分析了不同Cu含量对合金热稳定性的影响规律.随着热暴露时间延长抗拉强度快速下降,后期趋于稳定,延伸率先缓慢上升,后保持不变;随着热暴露温度的提高,合金的力学性能变化速度加快.随着Cu含量的增加,合金热暴露后的抗拉强度逐渐增大,塑性逐步降低;TEM分析可知,热暴露后该合金强度下降是由富铜相经过″θ→θ′→θ的转变,使得合金中的强化相完全析出、粗化所致.

Premature failure tends to occur to ZL702A alloy at a high temperature,which is used in the diesel cylinder head and body in our country,Al-7Si-xCu-0.3Mg-0.3Zn（x=1.5,2.5,3.5,w%） alloys were heat treated at 200 ℃ and 250 ℃ for 0～1 000 hours（thermal exposure）.In the experiment,the curves of their tension properties vs.thermal exposure time were drawn and their microstructure were observed by using an OM and a TEM.The influence of Cu content on the thermostability of these alloys was analyzed.It was found that the tensile strength decreased and elongation increased quickly initially in 100 hours and then the changes become constant.The change tendency was accelerated with the rise of thermal exposure temperature.The tensile strength increased and elongation decreased with the increase of Cu content after thermal exposure.Results observed with TEM showed that the changes mentioned above were attributed to the phase change of θ″→θ′→θ and subsequent growth of the Al2Cu phase.