FORMATION OF METAL MATRIX COMPOSITES AND INTERMETALLIC PHASES ON ALUMINIUM AA1200 DURING LASER ALLOYING

摘要

Laser surface alloying of aluminium AA1200 wasrnperformed with a 4.4kW Rofin Sinar Nd:YAG laser tornimprove it hardness and wear resistance. Alloying wasrncarried out by depositing Ni, Ti and SiC powders withrndifferent weight ratios on the aluminium substrate atrn10mm/s laser scanning speed. Surfaces reinfrorcedrnwith ceramics and intermetallic phases were achievedrnafter laser alloying. The phases observed in thernmicrostructure depend on the composition of thernalloying powder mixture. The reactions of Al with Nirnresulted in the in situ formation of Al_3Ni and Al_3Ni_2rnintermetallic phases. Some of the SiC particlesrndissociated and reacted with wither Al or Ti to formrnAl_4C_3, Al_4SiC_4, TiC or Ti_3SiC_2 phases. Si reacted withrnTi to form a Ti_5Si_3 phase. Surface hardness increasedrnwith increasing Ni content in the alloying powderrnmixture and a maximum of 13 times that of aluminiumrnwas achieved when alloying with 80wt%Ni + 15wt%Tirn+ 5wt%SiC. The increase in hardness was attributed tornthe intermetallic phases formed in the alloyed surfacernespecially the Al_3Ni_2 phase.