Surface treatments of Al-Si alloy castings by CO2 laser melting

Laser surface treatments of Al-Si casting alloys were carried out by CO2 laser. Laser surface melting was attempted to obtain surface layers with micro-crystalline structure. And further, laser surface alloying was carried out using silicon powder and cobalt base self-fluxing alloy powder as sources of alloying elements. JIS AC3A aluminum alloy and hyper-eutectic Al-24%Si alloy were used in this experiments. Multi-mode continuous wave beam was adopted. Laser irradiation was carried out in argon atmosphere in order to avoiding oxidation of specimens. With a beam scanning apparatus, an area in 8 mm width was irradiated. After the laser treatments, the large primary Si crystals of as-received materials are transformed to fine particles and dispersed uniformly in surface layer because of rapid solidification after melting. In the case of laser surface alloying using silicon powder, the porous alloyed layers consisting of needle primary Si crystals are formed. While, by cobalt base self-fluxing alloy powder, the alloyed layer develops a dense structure except some blow holes formed by some gas contained in the alloy powder or Al-Si alloy specimens.