VPPA Adding Welding Process, Microstructures And Properties Analysis Of AZ31B Magnesium Alloy Thick Plate

Because of the characteristics of lightweight, quake-proof, and electromagnetic interference-proof, highly damped, high thermal conductivity, and high electro negativity, etc, magnesium alloys are praised as the green engineering material in 21st century, and have a broad application prospect in automobile, motorcycle and aviation industries. With the wide use of magnesium alloy structure in manufacture, it is requested to investigate and apply the high-quality welding technique of magnesium alloy.However, the special physical and chemical properties of magnesium alloys lead to the poor weld ability, there are some flaws as coarse crystal, oxidation, evaporation, crack, pore etc with tradition welding process. Thus, it is a key of manufacture magnesium structure that choice a suitable welding process fit magnesium feature.The related issues of the variable polarity plasma arc welding (VPPAW) which has good prospects for the applications in the manufacturing of magnesium alloy components were investigated, and 8 mm AZ31B magnesium alloy plate butt-joint excrement were approached with VPPAW. The microstructure was investigated with optical microscopy. Mechanical characteristics were observed by scanning electron microscopy (SEM). Chemical components were analyzed by x-ray diffraction (XRD). Meanwhile, corrosion behavior mechanics of welded joint was discussed.The joints with good surface can be gained under proper matching of VPPA welding parameters. Application backing gas and front face shielding gas is the key of weld joint shape good or bad. Using small welding current, big plasma gas flow and high welding speed can obtain idea welding joint shape and mechanical property. Variation of welding parameters (welding current, plasma gas flow, welding speed) didn't influence the phase composition and will change grain size of microstructure of welding joint. The grains of welded joint are fine equ-axial crystal. Area coverage of HAZ narrow and exhibition composition feature of welding joint and base metal. There are no evidence element segregation at welding joints, some elements as Al, Mn, Zn etc solution atα-Mn basal body but there are little Al-Mn phase exist. Because of phase of Al-Mn exist, the element segregation andβ-Mg17Al12 can not be found in FZ, onlyα-Mg exists. Tensile strength of welded joints is lower than base metal, which up to 95% of strength of base metal. Tensile fracture of joints usually occurs in fusion area. Fracture pattern belong to brittle fracture. There are no pole and crack in welding joint. Hardness is the same whatever welding parameters variation. The hardness of fusion zoon higher weld joint and lower base metal The hardness have no change at fusion depth direction. Welding joint electrode potential is higher than base metal and has same corrosion ampere density, the corrosion resistance of melt zone was higher than that of the base material.