Laser Treatment of the Surface of Aluminum 8022 with the Presence of B4C Particles
Laser surface treatment of aluminium 8022 alloy is carried out. A 40 mm carbon film containing 5% B4C particles is formed at the workpiece surface prior to the laser treatment process. The carbon film reduces the surface reflection losses of the incident laser radiation and hosts uniformly distributed B4C particles at the surface. Morphological and metallurgical changes in the laser treated region are examined by using a scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The surface microhardness is measured and the residual stress developed at the surface is determined by using the XRD technique. It is found that dense layer is formed at the surface because of the high cooling rates and a columnar structure is observed in the region next to the dense layer. B4C particles remain in the solid phase in the surface region due to its high melting temperature. The presence of carbon film resulted in the formation of Al4C3 at the surface and AlN is also formed because of the high pressure nitrogen assisting gas. The microhardness of the treated surface is 440 ±20 HV, which is four times higher than that of the untreated surface (around 110 HV). The residual stress at the surface is compressive and it is –2.7 ±0.2 MPa.
Keywords: CO2 laser, aluminium alloy 8022, B4C, surface treatment, morphology, microstructure, microhardness, residual stress