Improvement in wear resistance of hyper-eutectic Al-Si cast alloy by laser surface remelting

Laser surface remelting of hyper-eutectic Al-20 and 30 mass%Si cast alloys with CO2 laser beam has been fined to improve the wear resistance of these alloys, A continuous wave CO2 laser beam with the power of 5kW was irradiated on these Al-Si cast alloy substrates under various defocused distance of laser beam with the argon gas shielding. The microstructure of the laser-remelted layer consisted of fine primary Si particles, primary alpha-Al matrix phase and fine alpha-Al-Si eutectic phase. The size of the primary Si particle decreased from 25 to 3 mum with the defocused distance also decreasing. Fine primary Si particles were distributed uniformly in the matrix of the fully remelted layer. The hardness of the laser remelted layer increased gradually with the decrease of the primary Si particle size, which reached 140 HV at about 5 mum in Al-30 mass%Si layer. The wear resistance of the remelted layer increased with increasing the hardness and decreasing the size of primary Si particle. The wear resistance of the remelted layer in Al-30 mass%Si cast alloy was better than that of the Al-20 mass%Si cast alloy. (C) 2003 Elsevier Science B.V. All rights reserved.