Study On Improving Mechanical Properties Of The Welds By Filling Magnesium Powder During Laser Welding5052Aluminum Alloy

Aluminum alloys, because of their excellent physical and mechanical properties,are widely used in aviation, aerospace, automotive, machinery manufacturing,shipbuilding, foundry industry and chemical industry. Laser welding，especially deeppenetration laser welding, is widely used in welding of aluminum alloys because of itsfollowing advantages: high energy density, big depth-width ratio, high weldingstrength, fast velocity, small deformation, good welds appearance. The application oflaser welding aluminum alloys can well solve such problems as the automatedcontrolling and precise input energy. Therefore，laser welding is gradually replacingthe traditional welding methods and becoming the most important means inmanufacturing and processing of aluminum alloys.However,the same as usingtraditional welding methods, such welding defects as the burning of the alloyingelements, porosity, oxidation and solidification cracks, etc., are also inevitably existedin laser welding of aluminum alloys, which can lead to the reduction of the weldsstrength. Among those welding defects, the burning loss of the alloying elements isthe main cause for reducing the tensile strength of the welds.In laser welding of aluminum alloys, the burning loss of magnesium will greatlyreduce such mechanical property of the welds as the tensile strength. In order toeliminate the negative effect of the burning loss of magnesium on mechanicalproperty of the welds, filling magnesium powder is adopted during laser welding ofaluminum alloys in this paper. First, the temperature field in laser welding ofaluminum alloys is simulated using the professional software SYSWELD. This workincludes modeling, meshing, selecting the heat source and verifying, pre-processing,calculating and post-processing program. Such simulation results as the temperaturefield, the stress field and the cooling rate at different welding velocities and laserpowers are obtained, which can provide some guidance for the subsequent weldingexperiments.Secondly, on the basis of analyzing the characteristics of laser welding aluminumalloys, the matching interval between laser power and welding velocity in laserwelding of aluminum alloy5052is determined through experiments. Based on theabove matching interval，the appropriate welding parameters of the fiber laser isselected, and a suitable laser welding parameters with filling magnesium is found. In addition，concerning the special properties of the magnesium and the problems existedpossibly in butt laser welding of aluminum alloy，the edge of the specimen is speciallydesigned，which can ensure good welding quality and provide preparations forsubsequent experiments of welding aluminum alloy with filling magnesium andmagnesium detection experiments.Finally, laser welding experiments is carried out using a fiber laser unit based onthe above-determined welding parameters with filling magnesium powder. Then，thetensile strength of the welds is tested，and the tensile strengths of the welds obtainedby laser welding with and without filling magnesium are compared. After that，usingEPMA，the contents of magnesium in the cross-section of the welds are measuredboth in the vertical and horizontal directions, and the effect of welding velocity on theburning loss of magnesium is experimentally investigated. Compared the tensilestrength of the welds under different magnesium contents, the relationship betweenthe content of magnesium in the welds and tensile strength is obtained. At last, usingmetallurgical analysis, the micro-structures of the welds are studied.