Influence Of Heat Treatment On Microstructure And Mechanical Properties Of As-Cast Al-Cu-Ti-(La) Alloy

With a wide application of aluminum alloys in aeronautic and astronautic, automotive as well as architectural industries, the higher mechanical properties are required for the alloys. Obviously, the investigation and development of new casting aluminum alloys is of both academic and practical significance. In order to provide a reliable theoretical foundation for engineering application of these aluminum alloys, both tensile properties and fatigue properties of the Al-5Cu-0.5Ti-(0.5La) alloys with different processing states have been investigated, and the influence of La and heat treatment on the mechanical properties of the Al-5Cu-0.5Ti-(0.5La) alloys are determined.The results of tensile experiments show that the solid solution and solid solution plus aging treatments can effectively enhance the yield strength and ultimate tensile strength of the Al-5Cu-0.5Ti-(0.5La) alloys. The elongation to failure and reduction in area for the Al-5Cu-0.5Ti-(0.5La) alloys get enhanced after solid solution treatments.The results of low-cyclic fatigue tests show that the Al-5Cu-0.5Ti-(0.5La) alloys subjected to different processing and treatment exhibit the cyclic strain hardening, softening and stability, which depends on the composition, heat treatment and imposed total strain amplitude. For as-cast Al-5Cu-0.5Ti alloy, the addition of La can effectively enhance cyclic deformation resistance of the alloys. For the Al-5Cu-0.5Ti alloy subjected to solid solution plus aging treatment, the addition of La decrease their cyclic deformation resistance at the higher total strain amplitudes. The solid solution plus aging treatment can effectively increase the cyclic deformation resistance of the Al-5Cu-0.5Ti-(0.5La) alloys. Moreover, the solution plus aging treatment can effectively improve the fatigue lives of the Al-5Cu-0.5Ti-(0.5La) alloys. A single-slope linear relationship between elastic and plastic strain amplitudes as well as reversals to failure is observed for the Al-5Cu-0.5Ti-0.5La alloys. For both as-cast and solid solution plus aging treated Al-5Cu-0.5Ti alloys, the relationship between elastic strain amplitude and reversals to failure also shows a linear behavior, but a bilinear relationship between plastic strain amplitude and reversals to failure is noted. The fractographic analysis results reveal that under tensile loading conditions, the Al-5Cu-0.5Ti-(0.5La) alloys show the typical ductile fracture, while under low-cycle fatigue loading conditions, the fatigue cracks initiate in a transgranular mode at the surface of fatigue specimens, and propagate transgranularly for the Al-5Cu-0.5Ti- (0.5La) alloys with different processing states.