Effect of ageing process on microstructure, corrosion behaviors and mechanical properties of Al-5.6Zn-1.6Mg-0.05Zr alloy

时效工艺对Al-5.6Zn-1.6Mg-0.05Zr合金微观组织、腐蚀行为及力学性能的影响

The influence of different ageing processes on the microstructure, corrosion behaviors and mechanical properties of extruded Al-5.6Zn-1.6Mg-0.05Zr(wt.%) alloy was studied in this work. The changes of morphology, size and distribution of MgZn_(2)precipitate with ageing temperature and time were revealed by optical and electron microscopy. Intergranular corrosion(IGC) and exfoliation corrosion(EXCO) tests were carried out to assess the changes in corrosion susceptibility of the tempered alloy, and some white spots on the surface of the sample aged for longer time were found to be precursors of pits. Electrochemical cyclic polarization test depicted the corrosion behavior under different tempers. Ageing influences on the mechanical behaviors of the alloy were revealed by evaluating its microhardness and tensile strength. The microscopic features of the strengthening phases determined by the ageing procedure directly affect the corrosion resistance and mechanical properties of the alloy.

本文研究了不同时效工艺对挤压态Al-5.6Zn-1.6Mg-0.05Zr(wt.%)合金的显微组织、腐蚀行为和力学性能的影响。采用光学和电子显微镜揭示了MgZn_(2)析出相的形貌、尺寸及分布随时效温度和时间的变化规律。通过晶间腐蚀(IGC)和剥落腐蚀(EXCO)试验分析了时效后合金的腐蚀敏感性变化情况,发现在经过较长时间时效后的试样表面出现的白点是发生点蚀的前兆;同时采用循环极化测试表征了不同时效态合金的电化学腐蚀行为。此外,测试并分析了经过不同时效工艺处理后试样的显微硬度和拉伸强度。时效过程中所形成的强化相微观特征直接决定了合金的耐腐蚀性和力学性能。