铸铝合金在潮湿大气中的腐蚀及其微观机制

Corrosion and Its Micromechanism of Aluminum Casting Alloy in Moist Atmosphere

用模拟湿热腐蚀试验方法在工业纯铝、ＺＬ１０２和ＺＬ１０９合金表面诱发腐蚀，用ＳＥＭ、ＥＤＳ和ＸＲＤ等实验手段观察和分析了铸铝合金中第二相和腐蚀产物的微观形貌及化学成分，研究了第二相与表面缺陷对铸铝合金大气腐蚀发生机制的影响．结果表明，在吸附了水分和侵蚀性Ｃｌ－的微观孔隙周围，由Ａｌ６Ｃｕ３Ｓｉ相粒子和铝基体构成的腐蚀微电池发生电化学反应，电位较负的Ａｌ首先发生溶解，导致了局部点状腐蚀；腐蚀产物中除了存在少量共晶硅、氧化铝外，主要由铝的不溶性氢氧化物构成．在０．５ｍｏｌ／ＬＮａＣｌ水溶液中的电化学测试结果表明，由于富铜Ａｌ６Ｃｕ３Ｓｉ第二相粒子的存在，在含侵蚀性Ｃｌ－的介质中，ＺＬ１０２、ＺＬ１０９合金比纯铝具有更强的腐蚀倾向．

Simulating moist heat corrosion experiments were conducted on commercial pure aluminum and aluminum casting alloy, ZL102 and ZL109 respectively. SEM, EDS and XRD were used to investigate microscopic morphology and chemical compositions of intermediate phases and corrosion products in aluminum casting alloys. Effects of surface flaw and intermediate phases on atmospheric corrosion were also investigated. The results show that the electrochemical reaction proceeds at the local galvanic cells constituted of Al 6Cu 3Si phase particles and Al matrix around the micro pore containing aggressive water. In the reaction, Al dissolves to produce local spotted corrosion. The corrosion products are mainly composed of insoluble aluminum hydroxides, including few eutectic Si and aluminum oxide. The results of electrochemical measurements in 0.5 mol/L NaCl solution also show that due to the existence of intermediate phase, Al 6Cu 3Si phase, ZL102 and ZL109 alloy have stronger corrosion trends than Al in Cl - ion containing solution.