In this study, it was tried to make an Al-Si clad layer with excellent wear resistant by scanning a pulsed Nd:YAG laser beam after printing silicon powder paste on the A1050 Al alloy surface. The microstructure and wear resistant of the clad layer were investigated according to the height of the silicon powder layer and the laser output power. An innovative method of using tape as a spacer to control the height of the silicon powder layer has been attempted. All the laser clad layers had a very fine microstructure. The silicon content in the clad layer was largely dependent on the height of the silicon powder layer rather than the laser output power. The average Si contents of A (107 ㎛ tape) and B (138 ㎛ tape) specimens were similar to 16.8 and 14.5 wt%Si, respectively, while C (197 ㎛ tape) specimens had an average Si content of 38.8 wt%Si. In the wear test, the average wear loss and the average friction coefficient were decreased with increasing the height of the silicon powder layer. The average wear loss of A and B specimens was similar to 6.8 and 6.2 mg, respectively. On the other hand, the average wear loss of C specimens was 3.5 mg, which indicated excellent wear resistance.

In this study, it was tried to analyze the effects of heat treatment temperature on the microstructure and wear characteristics of the hyper-eutectic Al-Si clad layer. The clad layer was produced by scanning pulsed Nd:YAG laser beam over the Si powder layer printed on the Al050 Al alloy base metal. The chemical composition of the clad layer was analyzed to be Al-20.8%Si. Despite the hyper-eutectic Al-Si composition, the clad layer mainly consisted of the very fine Al-Si eutectic microstructure without primary Si particles. The clad layers were heat-treated at 300 ℃, 400 ℃ and 500 ℃ for 5 hours. The specimen heat-treated at 300 ℃ retained the very fine Al-Si eutectic microstructure, but the continuity of Si particles in the Si network was broken. In the specimen heat-treated at 400 ℃, the Al-Si eutectic microstructure disappeared and fine Si particles were dispersed over the entire area. In the specimen heat-treated at 500 ℃, the melt-solidification traces disappeared and Si particles were grown considerably. The wear weight loss was the lowest in the as-cladded specimen and increased with the increase of heat-treatment temperature. Adhesive wear did not occur in the specimens as-cladded and heat-treated at 300 ℃, but occurred in the specimens heattreated at 400 ℃ and 500 ℃. The very fine Si networks in the Al-Si eutectic microstructure seemed to prevent adhesion of Al substrate to SKD 11 roll surface. Therefore, it was considered that there was no adhesive wear in the specimens which were as-cladded and heat-treated at 300 ℃.

A319 aluminum alloy containing 6.5% Si and 3.5% Cu as major alloying elements has been widely used in machinery parts because of its excellent castability and crack resistance. However it needs more wear resistance to extend its usage to the severe wear environments. It has been known that hyper-eutectic Al-Si alloy having more than 12.6% Si contains pro-eutectic Si particles, which give better wear resistance and lubrication characteristics than hypo-eutectic Al-Si alloy like A319 alloy. In this study, it was tried to clad hyper-eutectic Al-Si alloy on the surface of A319 alloy. In the experiments, Al-36%Si alloy powder was mixed with organic binder to make a fluidic paste. The paste was screen-printed on the A319 alloy surface, melted by pulsed Nd:YAG laser and alloyed with the A319 base alloy. As experimental parameters, the average laser power was changed to 111 W, 202 W and 280 W. With increasing the average laser power, the melting depth was changed to 142 ㎛, 205 ㎛ and 245 ㎛, and the dilution rate to 67.2 %, 72.4 % and 75.7 %, and the Si content in the cladding layer to 16.2 %, 14.6 % and 13.7 %, respectively. The cross-section of the cladding layer showed very fine eutectic microstructure even though it was hyper-eutectic Al-Si alloy. This seems to be due to the rapid solidification of the melted spot by single laser pulse. The average hardness for the three cladding layers was HV175, which was much higher than HV96 of A319 base alloy. From the block-on-roll wear tests, A319 alloy had a wear loss of 5.8 mg, but the three cladding layers had an average wear loss of 3.5 mg, which meant that an increase of 40 % in wear resistance was obtained by laser cladding.

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