Experimental Study On The Laser Welding Of Magnesium And Aluminum Dissimilar Metal

Compound structure of magnesium and aluminum have an extensive applicationprospect in aerospace and automotive industries, due to its low density and high specificstrength, ensuring the strength of structure while reducing its own weight, to achieve thepurpose of lightweight and reduce energy consumption and emissions, which is conducive toenvironmental protection. However, due to the small mutual solubility, the low melting point,the large and different linear expansion coefficient of magnesium and aluminum, resultingmagnesium and aluminum welding is very easy to produce porosity, cracks and brittleintermetallic compounds, which makes the magnesium and aluminum dissimilar metalswelding is very difficult. Laser welding is one of the preferably connection method formagnesium and aluminum dissimilar metal, because of its unique advantages such as highdensity of power, low heat input, concentrated heat, large depth-to-width ratio, narrow heataffected zone and small welding deformation.For the technical problems of magnesium and aluminum dissimilar metals is difficult toachieve reliability welding. In this paper, select AZ91magnesium alloy and6016aluminumalloy as the research object, design magnesium and aluminum laser lap welding test program,using the first-principle method of combining simulation with experiment based on thedensity functional theory, by means of using horizontal microscope, electron micro-hardness,scanning electron microscopy(SEM) and comes energy dispersive spectroscopy(EDS), X-raydiffraction(XRD), computer-controlled electronic universal testing machine, commercialsoftware of Castep and DMol to systemic study the weld surface formability of Mg/Al laserwelding, welded joint’s regional microstructure, hardness, fracture micromorphology, themain phase including its ductility,brittleness and thermodynamic stability, porosity and thejoint’s mechanical properties. The results are expected to provide an important fundamentalguidance for get a good performance of Mg/Al welded joints.To get the best weld surface formability as the goal, the effect of different weldingprocess parameters on weld appearance is analyzed, find the optimal process parameters,analysis of Mg/Al welded joint’s regional microstructure, hardness, fracturemicro-morphology and mechanical properties on optimal welding process. Based on the resultof phase detection of weld area, crystal cell model was optimized by density functionalmethod, the intrinsic mechanical properties of ductility and brittleness of Mg-Al intermetalliccompound is calculated by first-principle method. The Entropy, Enthalpy and Gibbs freeenergy of Mg-Al intermetallic compound in high temperature conditions is acquired, combined with the analysis of electronic structure, the stability of the phase structure ofMg-Al intermetallic compound and the inner mechanism of welded joint’s brittle fracture arediscussed.The porosities are common defects of magnesium and aluminum dissimilar metalswelding, the presence of porosity reduce the effective working area of the joint, and occurstress concentration, become the crack source of weld fracture, reduce the strength andductility of the weldment, which affects the quality of welding. Based on the result ofspectrum detection on different regions of the porosity defects, the element distribution of theaverage area, the interior region and the surrounding area of the porosity as well as the basematerial is studied, to find out the characteristic elements of affect porosity, explore the reasonof porosity formation and its suppression method.