高强铝合金轮辋失效分析

FAILURE ANALYSIS OF HIGH STRENGTH ALUMINUM ALLOY WHEEL

分析了重型车辆用高强度铝合金轮辋在实际使用过程中裂纹发生和发展的机理。采用拉伸试验机、金相显微镜、扫描电镜、能谱仪等手段详细表征了服役铝合金轮辋的力学性能、断口形貌、裂纹特征和腐蚀产物。分析结果表明,裂纹的形态呈"之"字形扩展,并且沿晶界断裂;裂纹起裂区和扩展区都存在腐蚀性元素S和Cl,具备典型的应力腐蚀特征。根据服役轮辋实际的装配和使用条件看,在腐蚀性介质条件下,铝合金轮辋与其配合的钢质锁圈存在电位差,接触产生电偶腐蚀。7A04铝合金经T6热处理后,在腐蚀环境中,其晶界存在的η相、S相和θ相等第二相相对于7A04基体晶粒本身为阳极而优先溶解,使得晶界成为活性路径,裂纹沿着这条活性路径扩展导致断裂。

The mechanism of cracks initiation and propagation of high strength aluminum alloy rims for heavy vehicles were analyzed. Tensile testing machine,optical microscopy,scanning electronic microscope and energy disperse spectrometer detailed characterization of the mechanical properties,fracture morphology,crack characteristics and corrosion products of aluminum alloy wheel respectively. The results show that the crack is look like the shape＂Z＂,expanding along the grain boundary and fracture;there are corrosive elements Cl and S at the crack initiation zone and crack extension area,with characteristics of typical stress corrosion. According to the actual assembly and service condition,it exist electric potential difference between aluminum alloy wheel and steel lock ring under the condition of corrosive medium,which will generate galvanic corrosion. After T6 heat treatment,there areηphase,S phase and θ phase on the grain boundary of 7 A04 aluminum alloy. In the corrosion environment,the matrix grain priority to dissolute itself as anodic,which makes the grain boundary become active path,crack propagation along the path lead to fracture.