Sn诱导Al−4Cu合金中θ′相向θ相的相转变机制及其对合金高温强度的影响

Sn-induced phase transformation mechanism fromθ′toθin Al−4Cu alloy and its influence on high temperature strength

通过显微组织观察和拉伸试验研究添加0.02%Sn(质量分数)对Al−4Cu合金在573 K高温热暴露过程(100 h)中θ′向θ相转变机制和高温强度的影响。研究结果表明,Sn微合金化能完全改变Al−4Cu合金在持久热暴露过程中θ′相向θ相的相转变机制。在未添加Sn的Al−4Cu合金中,棒状θ相在粗化后的盘状θ′相的表面形核和生长。然而,当添加少量Sn后,θ相首先在β-Sn颗粒上异质形核,然后形成粗大的针状相。由于Sn微合金化能提高Al−4Cu合金中θ′相的数密度并降低其尺寸,因此,Al−4Cu合金在T5状态下的室温和573 K高温下的屈服强度得到显著提高。然而,Sn微合金化能同时促进持久热暴露过程中θ′相向θ相的转变,导致Al−4Cu合金在热暴露后的高温(573 K)强度显著降低。

The effects of 0.02 wt.%Sn addition to Al−4Cu alloy on the phase transformation mechanism fromθ′toθphase during a long-time heat exposure at 573 K for 100 h and on high temperature strength were studied through microstructure observation and tensile test.It is found that Sn micro-alloying in Al−4Cu alloy completely changes the mechanism ofθ′→θphase transformation during the long-time heat exposure.In the alloy without Sn addition,rod-likeθphase nucleates and grows on the surface of coarsened disc-likeθ¢phase.However,with Sn-micro-alloying,θphase firstly heterogeneously nucleates onβ-Sn particles,and then grows into much coarser needle-like phase.Trace addition of Sn significantly increases the yield strength of T5-samples at both room temperature and 573 K,because addition of Sn increases the number density ofθ′particles and reduces its size.But,after the long-time heat exposure,the high temperature(573 K)strength of Al−4Cu alloy is severely degraded because Sn accelerates the phase transformation fromθ′toθphase.