Laser Surface Modification of Al-Cr Alloy Castings Produced by Centrifugal Duplex Casting

Effects of surface modification by a laser remelting process on the structure and hardness of surface composite castings of hyperperitectic Al-Cr alloys have been investigated. These castings were produced by either Centrifugal Duplex Casting(CDC process) or conventional centrifugal casting. The CDC process is applicable to the production of a tubular casting with an in-situ composite layer containing fine intermetallic crystals. On the other hand, there are coarse intermetallic crystals in the composite layer of the tubular castings produced by the conventional centrifugal casting. The intermetallic crystals in the laser-melted zone in each specimen were extremely refined regardless of their original size. However, many cracks were observed in the coarse intermetallic crystals near the melted zone on the specimen produced by the conventional centrifugal casting. On the contrary, no such defect were seen in the CDC specimens with finely dispersed intermetallic crystals. In these specimens, the hardness of the melted zone was about 50% higher than the substrate. Furthermore, addition of Cu was effective for the hardening of both of the substrate and the melted zone