THE MICROSTRUCTURE OF MG MODIFIED BY SURFACE ALLOYING WITH AN ALMG4.5MN WIRE

A TIG torch was used as the heat source for surface alloying of Mg. The alloying material in the form of an AlMg4.5Mn wire was directly fed into the melt pool. Both the microstructure and thickness of the alloyed layers are strongly dependent on the process parameters. When a higher current was used, the 2 mm thick Al-enriched layer produced on the Mg substrate consisted of dendrites of a solid solution of Al in Mg and a eutectic (Mg17Al12 + a solid solution of Al in Mg) distributed in the interdendritic spaces. Surface alloying of Mg at a lower current led to the formation a thinner alloyed layer comprising mainly an Al3Mg2 intermetallic phase. In the first case the hardness of the surface layer was 70-102 HV0.1, in the second 236-245 HV0.1.