| At present, vehicles are developing to be lightweight, high speed, safety, comfort, energy-saving and environmental protecting. It is trend to increase the aluminumzation of vehicles because of its lower density, high strength-to-weight ratio and so on. In this paper, the influences of heat treatment on the microstructures and tensile properties of A356 aluminium wheel are investigated by lots of analyzing and testing methods such as Optical Microscope (OM), Scanning Electron Microscope (SEM), Differential Scanning Calorimeten (DSC) and tensile testing.The relations between the solution treatment technology and the mechanical properties are investigated by variation of solution treatment parameter. .When the solution temperature is 535℃,the the mechanical properties including the tensile strength, the hardness and the elongation of the alloy rise first, then descend. When the solution time reach to 3.5～4.5h,the comprehensive properties are well matched.The results show that the A356 cast Aluminum alloys have good comprehensive mechanical properties by solution treatment for 3.5 hours at 545℃,and for the wheel rim the tensile strength is 251MPa,the hardness is 82HV,and the elongation is 12%; The tensile strength is 233MPa, and the elongation is 9% for the wheel breadth.So the technology of 545℃×3.5h is recommended .The relations between the aging time at room temperature and mechanical properties show that the time is suitable within 0～10h, but it can`t be over 12 hours. when the time is 2 hours ,the alloys have good comprehensive mechanical properties.The relations between the aging heat treatment technology and the mechanical properties are discussed by changing aging technology parameters. The results show that the mechanical properties go beyond the standard by aging treatment for 3 hours at the three temperature being set. So for A356, the tensile strength ,the hardness and the elongation can reach the highest simultaneously by aging treatment .When the solution technology is 535℃×4.5h,the aging time is at least for 3h.If the solution technology is 545℃×3.5h and the aging temperature is 135℃,when the aging time is 0.5h,the tensile strength and the plastic properties are very good .The time must be prolonged to 2.5～3.5h.If the aging temperture is 145℃,when the aging time is 1h,the comprehensive properties are well matched .So the time will be 1.5h～2.5h.The mechanical properties are compared between solution threatment of 535℃×4.5h and 545℃×3.5h.If the aim is to be good plastical properties ,the solution technology for 535℃×4.5h is suitable; and the solution technology for 545℃×3.5h is available for shortening the production cycle.The microstructure is observed through metallography microscope. The higher of the solution temperature and the longer of the heat preservation time are, the bigger the particles ofα(Al)grow, and the more Mg and Si would dissolve inα(Al) during the solution process. And the eutectic particles reduce obviously while Si particles become bigger.Α(Al)phases become grounder, the strength and hardness grow while the plastic properties drop.The fracture of tension specimens is observed on SEM. And the micro-appearance is typical plastic fracture. If the solution temperature and time are suitable, the dimples are big and deep. The plastics properties also are good. Either them less or higher than the optimal process parameters would lead to poor properties.The aging kinetics is discussed by means of DSC. G..P area is formed within 50～60℃, which attributes to vacancy's reuniting .β'-phase is formed within 250～300℃and deposited from the grain boundary or the screw dislocation because of Mg and Si atom enrichs in G.P area. The properties of the Al alloy will become bad whenβis formed over 300℃.
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