| Aluminum alloy is an ideal material to make the automobile lightened. Until now, there is certain distance between our country's welding technology and other developed countries on lightened materials welding, for example aluminum alloy, magnalium alloy, titanium alloy, plastic, chinaware and so on. In order to improve the competition of national auto industry, it is an imperative work to study the properties of RSW joints of aluminum alloy and other lightened materials.This experiment uses 6061 aluminum alloy provided by Beijing Benz-DaimlerChrysler Automotive Co,LTD which is a special kind of aluminum alloy sheet applied in auto-body of 300C , and adopts MF machine of spot welding which is similar with MF spot welding machine of Beijing Benz-DaimlerChrysler Automotive Co,LTD. First, the experiment studies how to optimize the design parameters for aluminum alloy sheet(0.9mm), then comparing to the RSW joints'properties of abroad part used in 300C auto, the same sheets are welded and compare and analyze mechanical properties and metal structure. At last, the effect of RSW, laser spot welding, RSSW on joint's properties and metal structure is studied. According to test result, it is known that when the welding current is 19KA, the electrodes press is 2.6KN, the welding time is in 90 to 120ms, it can obtain good quality welded joints and when the welding current is 21KA, the welding time is 120ms the electrodes press is in 2.7 to 3.0KN, the fatigue behavior of welded joints can be improved, but compared to the first one, the cut intension will be dropped. If the welding time is increased, the diameter of joint will be grown up but the properties will be fallen, as a result, the process of spot welding gets unstable. On larger electrode pressure, the fatigue time is improved, because the grains in metal inside structure become smaller, the diameter of air hole gets smaller and the amount of air hole will be reduced.The joint's cut intension is dropped largely because of air holes on the interface of RSW and laser spot welding and heat crack in laser spot welding joints, especially for laser spot welding joints. The welding power is direct proportion with surface sinking of laser spot welding, the power is bigger, the sinking is more serious. To adjust the design criterion of laser spot welding properly, it can reduce the surface sinking and make the effect of the surface sinking on oxidation film air hole and crack weaken in order to change the disabled form. The HAZ area of RSW is larger than the HAZ area of laser spot welding. The grains in HAZ of RSW will be grown up, as a result, the cracks and shrinking are produced between grains. They are harmful to pull intension of joints, so the joint's pull intension of laser spot welding is stronger than joints'of RSW.It is feasible to MF RSW of aluminum alloy in auto industry of our country, we must fasten the lightened steps of independent study in order to shorten the distance with developed countries.
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