预变形对Al-3.7Cu-1.6Mg合金断裂韧性的影响

Effect of pre-stretching on mechanical properties and fracture toughness of Al-3.7Cu-1.6Mg alloy

对固溶–淬火处理后的Al-3.7Cu-1.6Mg合金板材进行变形量分别为0、5%和10%的预拉伸处理,然后置于空气中进行自然时效,研究预变形对Al-3.7Cu-1.6Mg合金自然时效态的硬度、室温拉伸性能和断裂韧性的影响,利用扫描电镜(SEM)与透射电镜(TEM)观察合金的显微组织及断口形貌,研究其断裂机理。结果表明:该合金在淬火后引入预拉伸变形,可显著提高其自然时效态的硬度和屈服强度,同时抑制GPB区的形成,降低时效析出速率,并使峰时效时间延长;随预变形量从0增加至10%,Al-3.7Cu-1.6Mg合金的断裂韧性降低,这主要是预变形增加了基体内的位错密度,位错切割细小的GPB区粒子,大量滑移被抵消,造成变形过程中局部应力集中,从而形成微裂纹;由断口分析可知该合金的断裂类型为穿晶韧窝型断裂,且随预变形程度增大,韧窝直径和深度均增大。

The effect of pre-stretching on the hardness,tensile property and fracture toughness of Al-3.7Cu-1.6Mg alloy was investigated using scanning electron microscopy,transmission electron microscopy,hardness test,tensile test and fracture toughness test.Results indicate that the pre-stretching significantly increases the ‘natural aging’ hardness and the yield strength of the Al-3.7Cu-1.6Mg alloy.Meanwhile,the suppression of the formation of GPB zones by pre-stretching results in decreasing aging precipitation rate and prolonging the time to reach peak aging condition.The fracture toughness decreases when the pre-stretching increases from 0 to 10%.This is attributed to the fact that the interaction between the dislocations and the fine GPB zone particles is intensified by the increasing of pre-stretching,leading to large local strain concentrations and facilitating the formation of the micro-cracks.Furthermore,the decrease of the plasticity is detrimental to the crack propagation resistance and leads to the lower fracture toughness.The fracture surface observation showed that the alloy possesses a ductile transgranular character.Also,both the diameter and the depth of the dimples increase with the increasing of pre-stretching.