The Research On The Welding, Microstructures And Properties Of Magnesium Alloy AM60 Plates

In this thesis,the processing of gas tungsten arc(TIG) welding and CO2 laser beam welding(LBW)of magnesium alloy AM60 plates with 1.6 thickness were studied. The microstructure was investigated with optical microscopy. Mechanical properties were determined by standard tensile tests on small-scale specimens. Fractography characteristics were observed by scanning electron microscopy(SEM). Meanwhile,the characteristics of magnesium alloy AM60 welding were further analyzed through the differences between the joints of TIG welding and CO2 laser beam welding.The result indicated that the welding current and the welding wire were the important factors that affected the appearance of weld. Excessive welding current may result in burn through and undercut,and the excessive penetration of weld appeared with TIG welding without welding wire,the phenomenon was avoided when adding welding wire;It's found that Mg-AM60 1.6 mm-thick plates can be successfully welded by CO2 LBW.The joints strength of TIG welding was about 71% when the current ranging between 45 to 50A without welding wire,and was nearly 88% when using AZ91 welding wire with the current ranging between 50 to 55A.The LBW's was up to 94% with 0.8kW laser beam power,5L/min shield gas and -1mm clearance between focal point and surface.The microstructure was fine equiaxed grains in welded zone,which was shown consist ofα-Mg andβ-Mg17Al12,and theβphase existed along the boundaries and in the grains;While the HAZ was wide,the microstructures was coarse in the zone of TIG joints,and no visible HAZ zone was investigated in the CO2 LBW joints.It's found that the large number of pores in the joint seriously impacte the mechanical property of the joint,the pores may be reduced by adjusting the parameters and eliminating the factors of gas,but they can't be entirety avoided. Magnesium has higher hydrogen solubility in liquid than in solid. The difference in the solubility between the solid and liquid phase was major cause of the porosity of magnesium alloys during welding. The low melting element of magnesium alloy was easily to vaporize and the presence of porosity in the base metal coalesced and expanded,which was another cause. Because of low melting element existing magnesium alloy,hot-crack could be found in welds. Cleaning the plates,preheat...