Fatigue Performance And Heat Stability Of High-Strength Heat-Resistant Aluminum Alloy

In order to achieve a new high-strength Al alloy with a good performance of comprehensive mechanical property to meet the material requirement of HPD cylinder, three Al-7Si-xCu-0.3Mg (x=1.5,2.5,3.5wt%) alloys strengthened by heat-treating was designed and prepared. Their mechanical properties, fatigue properties and heat stabilities were tested.Fatigue property of Al-7Si-2.5Cu-0.3Mg alloy was tested through fatigue machine, and S-N curve of this alloy casted by metal-model and sand-model was drawn. The effect of Cu content to the alloy fatigue property was analyzed.Thermal exposure test conducted under 200℃and 250℃for 0-1000 hours. The influence of exposure time to the mechanical property and microstructure of Al-7Si-xCu-0.3Mg (x=1.5,2.5, 3.5wt%) alloys were studied. The effect of different Cu contents to the stability of alloys at high temperature was analyzed. With increasing of exposure time, their tensile strength obviously decreases comparing with that before exposure, and the elongation increases. The tensile strength increases and the elongation decreases with the increasing of Cu content. TEM shows that the change of mechanical property is caused by theθ"→θ'→θprogress of rich-Cu phase.The condition-fatigue limit of metal-model Al-7Si-2.5Cu-0.3Mg alloy is 96.5MPa and that for sand-model alloy is 36MPa, which is better than that of Al-7Si-1.5Cu-0.4Mg (702A-pro) alloy (25MPa). The fatigue property sequence of different Cu content (1.5Cu; 2.5Cu; 3.5Cu wt%) alloys is Al-7Si-2.5Cu-0.3Mg> Al-7Si-3.5Cu-0.3Mg> Al-7Si-1.5Cu-0.3Mg. SEM result shows that fatigue cracks mainly initiate on the defects parts and then grow and propagate until the sample fracture.