Investigations Regarding Electron Beam Surface Remelting of Plasma Nitrided Spray-Formed Hypereutectic Al-Si Alloy

Plasma nitriding of aluminum alloys is a suitable method for improving wear resistance because of the hard ceramic AlN layer formed. However, the surface's load-bearing behavior is greatly limited by the low hardness of the Al base material. New investigations regarding improved load support of the thin AIN layer examine the treatment sequence of nitriding and subsequent EB remelting. Because of its broad range of beneficial alloying elements (Si, Fe, Cu, Mg), a hypereutectic Al-Si alloy (DISPAL (R) S232) - made by spray forming - was used as the base material. The electron beam remelting process is carried out on samples with a nitride layer thickness of approx. 3 mu m. As a result of the newly formed phases, grain refinement, and oversaturation of the aluminum solid solution, the surface hardness beneath the nitride layer can be increased by up to three times compared to that of the initial base material. The estimated enhancement in load support is evaluated by unlubricated wear tests using a pin-on-disc configuration and scratch tests under constant loading conditions. Furthermore, the wear mechanisms are investigated by means of detailed SEM examination of the remelted surface layer.