The welding characteristics of Fe-30Mn-6Si and Fe-30Mn-6Si-5Cr shape memory alloys

After tungsten-inert gas (TIG) and laser welding, the microstructure, shape memory effect and chemical corrosion resistance of Fe-30Mn-6Si and Fe-30Mn -6Si-5Cr shape memory alloys have been investigated. Experimental results s how that the dendrite structures in the laser-welded zones are finer than i n the TIG-welded zones for both Fe-30Mn-6Si and Fe-30Mn-6Si-5Cr specimens. The Mn content in the TIG-welded zone of Fe-30Mn-6Si specimen is obviously reduced due to its vaporization during welding. The as-welded alloys still exhibit an excellent shape memory effect, with a variation of +/-10% due to welding. The corrosion resistance of welded zones is worse than that of ba se material for both Fe-30Mn-6Si and Fe-30Mn-6Si-5Cr specimens. The degrada tion of corrosion resistance is ascribed to the micro-segregation and weldi ng stress occurring within the welded zones. Meanwhile, the Cl- is more cor rosive than the NO3- for Fe-Mn-Si shape memory alloys. After annealing trea tment of 1100 degrees CX2 h for these welded alloys, the dendrite structure s in the welded zones disappear. The welded-then-annealed Fe-Mn-Si specimen s still maintain the excellent shape memory effect, and their corrosion res istance is improved due to the annihilation of micro-segregation and weldin g stress. (C) 2000 Elsevier Science S.A. All rights reserved.