Laser surface alloying of pure aluminum with iron and nickel via low power CO2 laser

Abstract

Aluminum is extensively utilized in industry due to its light weight, excellent workability and low cost. However, its wear resistance, hardness and mechanical properties are poor in comparison to steel. The technique of laser surface alloying was used to improve the aluminum surface properties such as hardness by modifying the composition and microstructure of the surface. A continuous wave (CW) CO2 laser beam was utilized for surface alloying in this research. The maximum output power of the CO2 laser is 27 W. The alloyed materials comprised of micro-powder of iron (Fe) and nickel (Ni). Pure aluminum substrate was pre-coated by a mixture of nickel and iron micro-powder with a ratio of 2:1. Hence, CO2 laser beam was irradiated on the pre-placed Fe-Ni powder to melt them together with the substrate at various times of exposure (10 - 60 s). The distance from output laser beam into the specimen was 20 cm. X-ray diffraction (XRD) and scanning electron microscope (SEM) were employed to analyze the alloying elements and study the microstructure of aluminum surface respectively. The hardness of alloyed surface was measured by using Vickers hardness tester. SEM analysis showed that the alloyed layer produced by a mixture of different elements is more homogenous and re-solidified. XRD results confirmed that several new intermetallic compounds such as Al5Fe2, Al6Fe, AlFe3, AlNi3 Al5FeNi, Al0.9Ni1.1 and Al76.8Fe14 are formed. The existence of these compounds confirmed that the aluminum surface has been alloyed. According to hardness test, the average micro-hardness of the treated surface increases approximately two times than the untreated surface. This technique is possible to alloy the surface of aluminum and improve its hardness