Effect of natural aging on Portevin-Le Chatelier effect of TiB2/7050 aluminum matrix composites
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研究了自然时效时间对TiB2/7050铝基复合材料塑性失稳效应(PLC效应)的影响.首先,对固溶水冷后进行不同时间自然时效的TiB2/7050铝基复合材料开展室温恒应变速率拉伸试验,然后分析平均应力跌幅、跌落时间、重加载时间以及临界应变,研究自然时效时间对PLC效应的影响,最后,利用扫描电镜观察拉伸断口微观形貌.结果表明,自然时效时间在1 h内,TiB2/7050复合材料的强度变化不大,超过1 h后,屈服强度和抗拉强度均有明显增加.PLC带类型随自然时效时间的延长由具有跳变性质的B类(0～1 h)逐渐向连续传播的A类(1.5 h)演变,再向具有阶梯传播特性的D类(2～4 h)演变.当自然时效时间超过1 h后,TiB2/7050铝基复合材料拉伸断口韧窝明显变浅,尺寸变小,这表明复合材料塑性随自然时效时间的延长而降低.因此,TiB2/7050铝基复合材料的固溶处理与人工时效的间隔不应超过1 h.
Effect of natural aging time on Portevin-Le Chatelier effect(PLC effect)of TiB2/7050 aluminum matrix composites was investigated.Firstly,room temperature constant strain rate tensile tests were carried out on the TiB2/7050 aluminum matrix composites,which was solution treated and water cooled,and then naturally aged for different time.Then the average serration amplitude,fall time,recovery time and critical strain were analyzed to study the influence of natural aging time on PLC effect.Finally,the morphology of the tensile fracture was observed by means of scanning electron microscope.The results show that the natural aging time within 1 h has a little effect on strength of the TiB2/7050 aluminum matrix composites,but the yield and tensile strengths increase significantly when the natural aging time is more than 1 h.The type of PLC bands evolves with the prolongation of natural aging time from the class B(0-1 h)with jumping nature to the class A(1.5 h)with continuous propagation,and then to the class D(2-4 h)with step propagation characteristics.When the natural aging time exceeds 1 h,the tensile fracture dimples of the TiB2/7050 aluminum matrix composites become significantly shallower and the size becomes smaller,indicating that the plasticity of the composite decreases with the extension of natural aging time.Therefore,the interval between solution treatment and artificial aging of the TiB2/7050 aluminum matrix composite should not beyond 1 h.
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