Study on Friction and Wear Properties and Mechanism at Different Temperatures of Friction Stir Lap Welding Joint of SiCp/ZL101 and ZL101

In order to achieve the goal of lightening the braking system of urban rail trains, SiCp/ZL101 and ZL101 plates were welded by friction stir lap welding (FSLW) to prepare a new type of brake disc material. The friction and wear properties of the friction-stir-processed composite material were studied at different temperatures (30 °C, 100 °C, 150 °C, 200 °C, 250 °C, 300 °C) to provide a theoretical basis for the evaluation of braking performance. The experimental results showed that the sliding friction processes at each temperature were relatively stable, the friction coefficients did not vary much and the average friction coefficients changed slightly, stabilizing at about 0.4. The wear extent and the depth of wear scars increased with the increase in the temperature, reaching the highest at 150 °C and then began to decrease. At room temperature, the wear forms were mainly oxidative wear and abrasive wear; as the temperature rose, under the cyclic shearing action of the grinding ball, the abrasive debris fell off under the expansion of fatigue cracks and fatigue wear was the main form at this stage. When the temperature reached 200 °C, it began to show the characteristics of adhesive wear; after 250 °C, due to the gradual formation of a mechanical mixed layer containing more SiC particles and oxides on the wear surface, it exhibited high-temperature lubrication characteristics, and the wear extent was equivalent to 35% of the wear extent at normal temperature, indicating that the composite material had good high-temperature friction and wear properties.