Laser Welding Research Of Fe-Mn-Si Shape Memory Alloy

Fe-Mn-Si shape memory alloys have a lot of advantages such as low-cost, moderate memory properties, high strong plastic and easy processing. At present, Fe-Mn-Si shape memory alloys are mainly used in fastener, which lags far behind its theory. In order to broaden its application range, the paper studies the welding performance of Fe-Mn-Si shape memory alloy by MOLD301-YAG laser welder.The paper discussed laser welding parameters which included current, frequency and pulse. Orthogonal experiment design method is used to determine the optimum laser double-side welding parameters. The tensile strength of the retro-welding samples is used as the indicators of evaluating laser welding performance. The tensile and bending fatigue test are used to study the mechanical properties of welded joint. With the method of metallographic microscope, scanning electron microscopy and micro hardness test, the relationship between the surface morphology of welding seam and the mechanical properties of welded joint is studied and the samples'fracture mechanism are revealed.Through the test of the tensile and bending of post-welding, it is found that the tensile strength and the cycle bending fatigue of Fe-Mn-Si shape memory alloy laser welding joints are close to or equal to the base metal. It is shown that Fe-Mn-Si shape memory alloy has good welding ability, and the welding samples still have good mechanical properties.From the cross-section of welding seam morphology under metallographic microscope, it is told that the mechanical properties of Fe-Mn-Si shape memory alloy welding seam are closely related to its cross-section. The seam welded by both sides can has good mechanical properties only if it has conditions such as wide welding seam, deep penetration, pool filling and "non-hollow".From SEM test, it is shown that the fracture surface of the welding seam presents obvious steps and river pattern, which indicates that the fracture is cleavage or quasi-cleavage type, brittle fracture.Compared with the fracture of the tensile test which is all in the welding seam, the fracture of welding samples which have excellent fatigue property in the bending fatigue test is located on one side of the welding seam. By micro-hardness test, the hardness of the welding seam is higher than that of base material. It is because that welding seam is quenched from the cold. The gradient distribution of the hardness, itself high hardness and low plasticity led the side of seam to stress concentration and fracture prior to welding seam.