Influence Of Heat Treatment On Microstructures And Mechanical Properties Of Al-Cu-Mg-La Alloy

As the metal materials with low density, high specific strength and excellentprocessing property, aluminum alloys are widely used in manufacturing industry,aerospace industry as well as building materials. In this investigation, different amounts ofLa were added into the Al-4.2%Cu-1.5%Mg alloy. The extruded and solid-solutionAl-4.2%Cu-1.5%Mg-xLa alloys are prepared by hot-extruding and heat-treatment. In orderto provide a reliable theoretical foundation for engineering application of the aluminumalloys, the tensile test and low-cycle fatigue (LCF) behavior as well as the observations onthe microstructures of Al-4.2%Cu-1.5%Mg-xLa alloys with as-extrude and solid-solutionstates were systematically investigated, and the influence of La and solid-solutiontreatment on the mechanical properties of the Al-4.2%Cu-1.5%Mg-xLa alloys aredetermined.The observations on microstructures reveal that the grains of both extruded andsolid-solution treated Al-4.2%Cu-1.5%Mg alloys get refined through adding moderatequantity of rare earth La. The results of the tensile experiments show that the addition ofLa with appropriate content can enhance the ultimate tensile strength, yield strength andimprove the plasticity of both extruded and solid-solution treated Al-4.2%Cu-1.5%Mg-xLaalloys. In addition, the solid-solution treatment can significantly improve both yield andultimate tensile strengths of the extruded Al-4.2%Cu-1.5%Mg-xLa alloys.The results of low cyclic fatigue tests in the paper reveal that cycle stress response ofboth extruded and solid-solution treated Al-4.2%Cu-1.5%Mg-xLa alloys, as the cyclicdeformation resistant of materials grows with the cycle-index, can mainly exhibit thecyclic strain softening and cyclic stability as well as cyclic strain hardening, which mainlydepend on the heat treatment, composition and the total strain amplitude which has beenimposed. Solid-solution treatment can significantly enhance the cyclic resistant todeformation of the extruded Al-4.2%Cu-1.5%Mg-xLa alloys and prolong the fatigue livesof extruded Al-4.2%Cu-1.5%Mg-xLa alloys. The addition of appropriate amount of rare earth La can effectively enhance the cyclic deformation resistance of both extruded andsolid-solution treated Al-4.2%Cu-1.5%Mg alloys and can prolong the fatigue lives ofextruded Al-4.2%Cu-1.5%Mg alloys as well.It can be certified in this paper that for both extruded and solid-solution treatedAl-4.2%Cu-1.5%Mg-xLa alloys, a single-slope linear relation can be observed betweenelastic strain amplitude, plastic strain amplitude and reversals to failure. And the results ofthe fatigue tests can all be described by the Coffin-Manson and Basquin equations.According to the observations and analysis of the fracture surface of the fatiguedspecimens under the condition of fatigue loading controlled by total strain amplitude revealthat, for both as-extruded and solution treated Al-4.2%Cu-1.5%Mg-xLa alloys, the fatiguecracks of the alloys initiate at the surface of fatigue samples in a transgranular mode andpropagate transgranularly as well.