Microstructure and strengthening mechanism of a 316 stainless steel coating prepared by high-speed laser cladding on an aluminum alloy plate

Aluminum alloy plates show great potential in energy storage and transportation applications. Nevertheless, the low surface strength of aluminum alloy plates negatively impacts their performance and safety. Aluminum alloys exhibit characteristics such as a low melting point, high reflectivity, and a rapid dilution rate, posing significant challenges for laser cladding coatings. This paper presented the surface modification mechanism of aluminum alloy plates. A stainless steel coating was successfully prepared on the surface of aluminum alloy substrates by using high-speed laser cladding technology. The microstructure, microscopic morphology, and microhardness of the coatings were conducted. The surface and sides of coatings were analyzed by XRD, SEM, EBSD, and microhardness testing, respectively. It is found that larger cellular crystals and carbides predominate at the junction of the substrate and the coating. The middle part of the 0.5-mm coating from the connection and the heat-affected zone are mainly dendritic crystals. The top of the 1-mm coating from the connection is mainly fine crystals. This means that local grain refinement occurs in the stainless steel coating via high-speed laser cladding. There is a transformation of FCC to BCC in the coating. Moreover, the cross-section of the coating exhibits a relatively high microhardness, ranging from 517 to 679 HV. The microhardness at the substrate is measured at 67 HV. The maximum microhardness of the coating is ten times that of the substrate. The bottom of the coating maintains a relatively high microhardness due to the presence of a large amount of carbides. The microhardness of the coating gradually increases from the middle to the surface of the coating. This is primarily attributed to solid solution strengthening and fine grain strengthening mechanisms. Columnar crystals at the metallurgical bond between the substrate and the coating transform into fine grains at the top, leading to a gradual refinement of the microstructure. High-speed laser cladding technology facilitates the enhancement of surface properties and the improvement of surface strength in traditional aluminum alloys.