Effect of samarium on the high temperature tensile properties and fracture behaviors of Al-Zn-Mg-Cu-Zr alloy

The Al-6.7Zn-2.6Mg-2.0Cu-0.1Zr alloy is modified by Sm for the purpose of improving its mechanical properties at high temperatures. According to the results, the as-cast structure can be refined through 0.3% Sm modification treatment, and finer precipitates can be obtained after aging. In the meantime, with the addition of Sm, a new high melting point Al10Cu7Sm2 phase is formed, the initial decomposition temperature of the alloy is raised, and the thermal stability is enhanced. As indicated by the tensile test results at room temperature and high temperatures, the strength of the modified sample was improved compared with the unmodified alloy. According to fracture surface analysis, ductile fracture conforms to the fracture characteristic exhibited by the modified alloy at room temperature and high temperatures. The improvement on high temperature strength of the modified alloy is attributed largely to a combination of grain refinement, precipitation strengthening and heat resistant phase to grain boundary pinning.