CO₂ Laser Welding Research Of Fe-Mn-Si Shape Memory Alloy

As a new type of function materials Fe-Mn-Si shape memory alloys are famous for their excellent memory effect and mechanical properties. At present, the research of Fe-Mn-Si memory alloys is still relatively limited in the area of the shape memory effect. In order to further broaden its application range, the paper studies the CO2 laser welding performance of Fe-Mn-Si alloy by CO2 gas laser welder, tensile test, metallographical, scanning electron microscopy, X-ray diffraction and micro-hardness analysis from the connectivity with their own and between the Fe-Mn-Si alloy with other metal materials to analyze the connection performance.This paper selects the most important CO2 laser welding process parameters which are power, welding speed and defocusing distance, and makes the tensile strength of welded joints as welding performance evaluation indicators. This paper can be drawn that the power has the most important influence for the tensile strength of the sample in the selected range through range by orthogonal experimental design methods from variance analysis, but the defocusing distance has minimal impact. For the welding lmm thick Fe-Mn-Si alloys of no additional welding material, when the respect power, speed and defocus of the CO2 laser welding parameters are 1600W,2.2m/min,0.6mm, respectively, the tensile strength of welded joint is highest up to 928MPa, which is up to 93.5% of the base metal tensile strength. It is revealed that Fe-Mn-Si shape memory alloys have good welding ability.By the metallographical observation and tensile test it is found that the tensile strength of welded specimens is decline because weld morphology which is the "V", too broad and lack of penetration, etc, however, the tensile strength is high when the weld morphology showed a hyperbolic shape. From the view of weld organization morphological, the weld center organizations are small equiaxed, and the range of fusion zone are thick cellular crystal. The weld organizations are smaller, which tensile strength is higher and its toughness is better. The fracture location of tensile sample occurred in the near of the weld fusion zone.By the fracture scanning electron microscopy analysis it is found that the fracture of Fe-Mn-Si alloy shows many small dimples, and has clear necking phenomenon before breaking, which fracture format is the plastic fracture. The fracture of weld sample is mainly characterized by river pattern, and appeares some steps sometimes. This form of fracture is quasi-cleavage, which is belongs to brittle. It is because that the weld fusion zone has shown thick crystal after laser welding.By the micro-hardness analysis it is found that the weld center has the highest hardness value, and the near of fusion zone has the lowest hardness value. This is mainly because the material has produced cold-hardening when it rapidly heating and cooling after laser welding, and it increased the hardness of the weld center. In morphology, the grain is coarse in the near of fusion zone, and showing cellular crystal, so which the hardness is low.By the weld performance between dissimilar metals with Fe-Mn-Si alloy research it is found that the welding ability between Fe-Mn-Si alloy with 304 stainless steel is well, and with 70Mn steel is poor. It is because the chemical of Fe-Mn-Si alloy is similar to the 304 stainless steel but is far to the 70Mn steel.