Research On Numerical Simulation Of The DE-GMAW Welding Process Of Magnesium Alloy Missile Cabin And Tail

Magnesium alloy is one of the lightest metallic structural material at present,which has very high specific strength.It has been widely applied in these fields of weaponry,electronic products,automobile,aerospace and so on.It already became a focus which has attracted wide attention and research at home and abroad.Because magnesium alloy has the characteristics of close-packed hexagonal structure,the independent slip system is less at room temperature,so the deforming process of magnesium alloys is difficult,especially the welding process.The traditional welding methods are more and more difficult to meet the requirement of high quality and efficiency.Many high quality and efficient welding methods have been put forward to weld magnesium alloy,one of them is Double-electrode gas metal arc welding,it’s short for the “DE-GMAW”.In the DE-GMAW welding system,the welding current act on magnesium alloy wire is larger,so deposition efficiency of wire is increased,and the welding current act on the parent metal is equal to the welding current which act on the wire minus the bypass current,thus can control the heat input by adjusting the by-pass arc parameters.Therefore,the principle of DE-GMAW welding process is completely different from the traditional welding technology,this high efficient method can improve the deposited rate and welding quality,and has no special requirements for welding equipment,so the cost is low.Excessive welding stress tends to cause fatigue fracture and stress corrosion cracking of magnesium alloy welded joints,which seriously affects the bearing capacity,stability and service life of magnesium alloy welded structures.The thin plate welded structure is widely used in the weapon equipment,welding deformation of thin-plate structure which caused by welding stress is an important factor affecting the quality of welded structure with thin plate,therefore,it has important practical significance to optimize welding process to improve the quality of welding thin plate.In the past,the optimizing welding process was mainly carried out by experimental exploration.With the research and development of welding thermoplastic theory and the progress of computer simulation technology,it is able to predict and analyze the welding deformation of thin plate welded structure and optimize welding process.This paper use MSC.marc finite element simulation software to research the welding process of the AZ31 B magnesium alloy missile’s capsule girth weld and tail fillet weld,and the welding process of DE-GMAW is carried out use numerical simulation technology.First of all,this paper investigate the effect of Single pass welding and Double layer with two passes welding,different welding heat input,different welding preheat and interpass temperature on welding heat cycle curve,field of welding temperature and stress and welding residual stress.The results show that the position which get closer to welding heat source,the temperature rise faster and can get a higher temperature peak,in the meantime get the slow cooling rate.Double layer with two passes welding,the latter layer has heat treatment effect on the previous layer,which reduces the residual stress and it is lower than single pass welding.With the increase of welding heat input,the temperature peak,plastic deformation widths and longitudinal residual stress of girth weld are increase,but the lateral residual stress increases not obvious.Preheating can raise the temperature of the whole welding workpiece,so that it can reduce the temperature difference between workpiece and the maximum temperature which obtain during the welding process,and the corresponding thermal stress also was reduced,this help to reduce the longitudinal residual stress,but a little help to reduce transverse residual stress.By setting preheat and interpass temperature as 200 can effectively reduce the longitudinal residual stress.℃Secondly,this paper study the welding sequence of the fillet welds on both sides of a single tail to learn the distribution of structure deformation after welding,and according to the optimum welding sequence to make numerical simulation analysis on all tails’ fillet welds.The results show that the four kinds of welding sequence model obtain same deformation trend,are the tail shrink along the Z axis direction and move along Y axis direction.The residual deformation of four welding sequence are 3.221 mm,2.610 mm,3.573 mm and 2.423 mm,respectively.When the welding sequence are 1 and 3,the heat sources moving in the same and opposite direction at the same time,so the transverse residual stress of them is larger than the welding sequence 2 and 4,both 2 and 4 are welding respectively.The transverse residual stress distribution obtain by welding sequence 1 and 3 are extremely uneven.The transverse residual stress curve obtain by welding sequence 2 and 4 is closer and the trend of change is relatively stable,and the welding deformation,equivalent stress and transverse residual stress obtain by welding sequence 4 is the smallest and most stable.Finally,the welding sequence 4 is used to simulate all the four tails’ eight fillet welds of the missile.The results show that the transverse residual stress distribution trend is approximately same and keeps at about 150 MPa,so this welding sequence is more reasonable.