Impact of Rotational Speed in Fast Multiple Rotation Rolling on the Microstructure and Tribological Properties of A390 Alloy Friction-Surfaced Coatings
摘要
This study investigates the influence of rotational speed during fast multiple rotation rolling (FMRR) on the microstructural evolution and tribological performance of A390 aluminum alloy coatings fabricated by friction surfacing. Four rotational speeds—400, 600, 800, and 1000 rpm—were applied under constant load and traverse speed. Results reveal that the coating thickness decreased from 2.3 mm at 400 rpm to 1.7 mm at 1000 rpm, while the maximum width increased from 26.2 to 30.9 mm. The highest coating efficiency (37.1%) and most uniform material flow were achieved at 800 rpm, corresponding to an interface temperature of approximately 416 °C. Microstructural analysis demonstrated significant refinement of primary silicon particles and dynamic recrystallization of the aluminum matrix, with the minimum average grain size of 2.1 ± 0.6 µm observed at 800 rpm. Simultaneously, Al2Cu precipitates were refined from 1.5 ± 0.1 µm at 400 rpm to 0.6 ± 0.2 µm at 800 rpm, followed by partial coarsening (1.3 ± 0.2 µm) at 1000 rpm due to overaging. Mechanical evaluations showed that the microhardness of coatings increased by up to 27.6% compared with the as-cast alloy, with the peak surface nano-hardness (~ 6.9 GPa) and Young’s modulus (~ 137 GPa) also recorded at 800 rpm. Tribological testing revealed a minimum wear rate at 800 rpm—approximately 45% lower than that of the consumable rod and 75% lower than the AA1010 substrate.