采用传统熔炼铸造法制备Al-Zn-Mg-Cu合金,通过晶间、剥落、应力和电化学腐蚀实验,结合金相显微镜、扫描电镜和透射电镜等表征手段,研究再结晶和结晶相对合金腐蚀行为的影响.结果表明:再结晶程度更低和残余结晶相更少的Al-Zn-Mg-Cu-Zr合金具有更好的耐腐蚀性能,腐蚀 48 h后的剥落腐蚀等级为EB,弯曲张应力为 522 MPa时的应力腐蚀裂纹萌生时间为 30 min,电化学腐蚀速率变慢.超高强铝合金的腐蚀分为 3 个阶段:腐蚀初期,点蚀在残余结晶相(S相)和晶界析出相(η 相)周围发生;腐蚀中期,点蚀沿大角度晶界发展为晶间腐蚀,裂纹在 S 相附近形成并沿大角度晶界扩展,导致应力腐蚀开裂;腐蚀后期,腐蚀产物膨胀以及晶间腐蚀和应力腐蚀开裂的共同作用引发剥落腐蚀.残余结晶相和再结晶对合金腐蚀性能有不利影响,基体中残留的 S 相为腐蚀提供了发生位点,η 相在再结晶形成的大角度晶界上连续分布,为晶间腐蚀和应力腐蚀裂纹扩展提供连续通道.
Local corrosion behavior of ultra-high-strength aluminum alloys
Al-Zn-Mg-Cu alloys were prepared by the traditional melt casting method.The effects of recrystallization and crystalline phase on the corrosion behavior of Al-Zn-Mg-Cu alloys were investigated through intergranular,exfoliation,stress,and electrochemical corrosion experiments,combined with characterization means such as metallurgical microscopy,scanning electron microscopy,and transmission electron microscopy.The results show that the Al-Zn-Mg-Cu-Zr alloy with lower degree of recrystallization and fewer residual crystalline phases has better corrosion resistance,the grade of exfoliation corrosion after 48 h of corrosion is EB,the time of stress corrosion crack initiation with bending tensile stress of 522 MPa is 30 min,and the rate of electrochemical corrosion becomes slower.The corrosion of ultra-high-strength aluminum alloy has three stages:at the early stage,pitting corrosion occurs around the residual crystalline phase(S phase)and the grain boundary precipitate phase(η phase);at the middle stage,pitting corrosion develops into intergranular corrosion along the high-angle grain boundary,and cracks are formed in the vicinity of the S phase and expand along the high-angle grain boundaries,leading to stress corrosion cracking;at the late stage,the expansion of corrosion products as well as the combined effect of intergranular corrosion and stress corrosion cracking trigger the exfoliation corrosion.The residual crystalline phase and recrystallization have a detrimental effect on its corrosion performance,the residual S phase in the matrix provides a site for corrosion to occur,and the η phase is continuously distributed on the high-angle grain boundaries formed by recrystallization,which provides a continuous channel for the expansion of intergranular corrosion and stress corrosion cracking.
万方数据
维普
