| The application of aluminium alloy in the automobile is more and more extensive, and welded joint is the weak position in the automobile body structure. Through the experiment, the hardness distributions and the strength has been examined and the relation of these and thermal cycle of welded process has been examined also.The appraising method of strength of welded joint has been search through the experiment and finite element analytical method. The result shows :In oder to get good welded joints,these measures has been adopted: a) puting copper boards under the butt joint and T type joint before welding experiment, b) puting copper bushing pipe in rectangle pipe (welding work piece) and guiding arc board beside the welding seam end before welding T-joints RHS(rectangular hollow section).Combining other suitable welding process parameters, good welded joints can be manufatured .Effects of artificial ageing on the hardness distributions and the strength were examined for 6063 aluminium alloy joints welded by two heat inputs. The hardness of the welded joint can be increased by artificial ageing, especially in the weld metal and heat-affected zone near the fusion line the hardness equal to or more than that of base metal can be obtained, so as the strength of overall joints can be increased. But there are softenning heat affected zones of 4-5 mm still. The determination of thermal cycle in heat-affected zone show that, in the zones with the peak temperature greater than 350 °C, the hardness can be fully recovered by artificial ageing, for overageing zone with the peak temperature between about 250 and 350°C, the hardness can't be fully recovered. For a heat-treatable aluminium alloy the reason of HAZ softening is dissolution and growth of the strengthening precipitates in certain range of temperature,It has been also found that the fracture position of all joints lie in overageing zone through drawing experiment.In order to appraise the strength of the T type joint of fillet weld by drawing experiment, two kinds of T type draw samples has been designed by analytical method of finite element in this paper, and the experiment scheme and sample clamping have been designed ,and the drawing experiment has been done by these designs . The experiment can be used to study strength and fracture mechanism of T-jont.Welded T-joints RHS was used widely in the space frame structure ofAluminium alloy body of motor car. By experiment and finite element analysis method, the deformation limit and ultimate strength of welded T-joints in RHS sections were investigated, and analyzed the causes of effect strength of T-joint. The result shows: a) steel tube joint deformation limit that Lu et al proposed can be use in the aluminium alloy T-joint RHS, but because the elastic mould amount of the aluminium alloy is much lower than the steel, so its ultimate strength is overly conservative; b) the T-joint restraint form has greater influence on the ultimate strength ,the loaded form has certain influence on the ultimate strength.By the finite element analysis method , the material yield strength of the aluminium alloy has a certain influence on ultimate strength of T-joint RHS ,pis the smaller and its influence is smaller. c) the width of softenning zone will have a certain influence on ultimate strength, the softenning zone is wider and the ultimate strength is smaller,and the softenning zone influence is more obvious when the width is within 7mm, the material strain- hardening properties has small influences on ultimate strength . d) the elastic mould amount of material has a tremendous influence on ultimate strength.
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