Research On Laser Welding Of FeMnSi Memory Alloy/304 Stainless Steel

FeMnSi memory alloy has the characteristics of stress self-accommodation and shape memory simultaneously,which makes it presents excellent mechanical properties.304 stainless steel is one of the widely used metal materials.If these two materials are welded together,structural functional components with excellent mechanical properties could be obtained by utilizing the shape memory and stress self-accommodation characteristics of FeMnSi alloy.This paper investigates the welding for the dissimilar materials:FeMnSi memory alloy and 304 stainless steel.The process parameters,mechanical and microstructure properties of welding seam are studied by laser welding experiment of FeMnSi memory alloy/304 stainless steel joints,and the temperature and stress fields of FeMnSi memory alloy/304 stainless steel during the welding process are simulated and analyzed by finite element method.By the single factor experiments,the effects of current,frequency and defocus on the weld width and joint tensile strength are investigated.The results show that the changes of current,frequency and defocus lead to fluctuating welding heat input,thus causing variations of tensile strength and weld width.Under the test conditions,the tensile strength increases with increasing laser current,and firstly increases and then decreases with increasing frequency.In addition,the tensile strength is relatively high when the defocusing distance is 5mm.According to the orthogonal test analysis with tensile strength as performance index,the optimum technological parameters are 185A current,13Hz frequency and+6mm defocus.The welded joint breaks at the stainless steel side and the tensile strength reaches 697MPa,which is up to 86%of FeMnSi alloy tensile strength and obviously exceeds that of 304 stainless steel welded joint.The average microhardness of FeMnSi memory alloy/stainless steel weld is HV223.35,which is higher than that of the stainless steel and slightly lower than that of the FeMnSi’memory alloy.When the bending strain is 6%,the bending fatigue number of FeMnSi memory alloy/stainless steel heterogeneous joint is slightly higher than that of the stainless steel.Finite element simulation on the welding temperature field of FeMnSi memory alloy/stainless steel shows that in the process of laser heat source close to and away from the nodes in the weld joint,rapid heating and cooling occurs.The temperature is higher only in the welding seam,while lower in the base metals.The isotherms on the FeMnSi memory alloy side are denser than those on the other side,and the temperature on the stainless steel side drops faster in the cooling stage.Despite the weld center,the longitudinal residual stresses are compressive at both ends of the weld seam,while tensile at the rest of the weld seam,and correspondingly,the residual stresses away from the weld seam are compressive.The transverse residual stresses are tensile at the seam center,and gradually transferred to compressive at the region away from the weld.The bilateral asymmetry of longitudinal residual stresses of FeMnSi memory alloy/stainless steel dissimilar material joint is more apparent than that of the transverse residual stresses.