Formation of Ni-rich aluminide layers on an A356 aluminum alloy by a combined electroplating/laser alloying treatment: Microstructure and tribological characteristics

Abstract

To improve the tribological properties of A356 aluminum alloy, a two-step surface treatment was used to produce a Ni-rich aluminide layer on the alloy surface. At first the A356 alloy specimens were electroplated using pure nickel. To study the effect of nickel content, layers with two different thicknesses were produced. Then, the layers were melted by a pulsed Nd:YAG laser. Microstructural evaluations were done using optical and scanning electron microscopy, energy-dispersive spectroscopy, and X-ray diffraction. Wear tests were performed by a pin-on-disk tribometer. Microstructural examinations revealed that alloying led to the formation of Al-Ni intermetallics with dendritic and seaweed morphologies. Furthermore, layer with lower nickel content was mainly composed of Al3Ni intermetallic, while in the case of layer with higher nickel content, Al3Ni2 phase was also detected. Wear tests results showed that alloying enhanced wear resistance of substrate, and the best wear resistance achieved for the layer with higher nickel content. Formation of intermetallic phases was the main reasons for higher wear resistance of layers. Study of worn surfaces indicated delamination as the dominant wear mechanism of substrate, whilst for layers with high and low nickel content adhesion and adhesion-abrasion were proposed as the main mechanisms, respectively.