| In this paper, YAG pulsed solid-state laser and CO2 laser were used for the welding performance study of Fe-17Mn-5Si-10Cr-5Ni memory alloy. The orthogonal test was carried out to select the welding parameters, the mechanics performance testing and weld microstructure observation and analysis method were used for the in-depth and systematic study of mechanical properties of welding joints and weld microstructure, and based on finite element analysis software ANSYS, the numerical simulation was carried out for the temperature and stress field of laser welding of Fe-Mn-Si memory alloy.It was obtained in the orthogonal test that the optimal parameters for YAG laser welding of 1 mm thick Fe-17Mn-5Si-10Cr-5Ni memory alloy plate were current I=100 A, frequency f=3 Hz and pulse width T=15 ms. The optimal parameters (power, speed, defocus amount) for CO2 laser welding of 1 mm and 2 mm thick Fe-17Mn-5Si-10Cr-5Ni memory alloy plate were P=1600 W, v=800 mm/min, z=+0.6 mm and P=2000 W, v=250 mm/min, z=-0.5 mm. The optimal parameters for CO2 laser welding of lmm and 2mm thick Fe-17Mn-5Si-10Cr-5Ni memory alloy plate and 304 stainless steel plate were P=1800 W, v=800 mm/min, z=+0.6 mm and P=2500 W, v=800 mm/min, z=-1 mm.The stress self-accommodation characteristic of Fe-17Mn-5Si-10Cr-5Ni memory alloy made the resistance to bending fatigue of welding joints high, and in the case of the control strain ε≈5%, the number of bending fatigue of welding joints was not less than 430 times, far greater than the 50 times of the contrastive 304 stainless steel.The study showed that the laser weld appearance directly affected the tensile strength of welding joints of Fe-17Mn-5Si-10Cr-5Ni memory alloy. The YAG laser weld showed significant characteristics of heat conduction, while CO2 laser weld showed significant characteristics of keyhole welding. There was no significant heat affected zone near the CO2 laser weld fusion zone, and the weld microstructure produced symmetric crystals from fusion zones at both sides to the weld center and the crystalline grains gradually transformed from cellular dendrite into dendrite microstructure from the weld fusion zone to the weld center, and the width of the fusion zone was about 80 um; In the microstructure of and near the weld, there was s martensite phase, which was caused by the γâ†'ε martensitic transformation induced by the tensile residual stress in the welding process. At the same time, such ε martensitic transformation relaxed the welding residual stress.The CO2 laser welding test of dissimilar joints of Fe-17Mn-5Si-10Cr-5Ni memory alloy and 304 stainless steel showed that the crystals were symmetrically distributed on both sides of the joint weld center. They were flat crystals, cellular crystals and cellular dendrites in sequence, but the crystalline grains in the weld near the side of 304 stainless steel had a significantly smaller grain size than those near the side of Fe-17Mn-5Si-10Cr-5Ni memory alloy. The welding seam center had good histocompatibility, dendrite crystals were dominant, and there were small differences in the crystalline form. At Fe-17Mn-5Si-10Cr-5Ni memory alloy close to the side of the weld, ε martensite phase was also found, which was caused by the γâ†'ε martensitic transformation induced by the tensile residual stress; The full cyclic fatigue fracture of dissimilar joints consisted of the extension zone and instantaneous fracture zone. In the former, there were fatigue striations, dissociation steps and some arc tearing ridges, showing typical quasi-cleavage brittle fracture characteristics, and in the latter, there were a lot of dimples, showing plastic fracture characteristics; The distribution of dissimilar joint weld elements was in zones obviously, the distribution mode was related to the unique keyhole effect of laser welding, and the weld center metal was still Fe-Mn-Si memory alloy.The numerical simulation results of CO2 laser welding finite element of Fe-17Mn-5Si-10Cr-5Ni memory alloy showed that the core temperature of welding heat source reached 2,500 ℃, and the maximum temperature at 2 mm from the welding seam center was less than 750℃, below the solid-state phase transition temperature of the material, therefore the laser welding had a small heat affected zone. After cooling, there was residual tensile stress in the weld, and its value was close to the yield limit of Fe-Mn-Si memory alloy, which met the condition of stress-induced γâ†'ε martensitic transformation. |
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