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Microstructural Refinement and Improvement of Microhardness of a Hypoeutectic Al-Fe Alloy Treated by Laser Surface Remelting
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1  Department of Manufacturing and Materials Engineering, University of Campinas UNICAMP, Campinas, SP, 13083-860, Brazil


In the laser surface remelting (LSR) treatment, only a small region is heat affected, surpassing the melting temperature, and followed by a rapid cooling at 105 – 108 K/s, producing an extremely refined microstructure. The laser treated region shows a more homogeneous microstructure and better mechanical properties than the substrate. The LSR is a great technique to improve the Al alloys properties, increasing the hardness and wear resistance without modifying the composition of the material. Iron is commonly found as an impurity in Al-based alloys, but in the 2618 commercial alloy, around 1wt.% of Fe is intentionally added to improve the high temperature strength and the corrosion resistance. In addition, Al-Fe based alloys are used in packaging, architectural sheets and high voltage cables. In this work, LSR experiments were performed, with a CO2 laser operating in a continuous-wave mode, to investigate the influence of process parameters on the treated surface of an as-cast Al-1wt.%Fe alloy. These parameters cover work distance (z = 6 and 8 mm), laser beam speed (v = 500, 750 and 1000 mm/s) and laser average power (P = 400, 600 and 800 W), setting a total of 18 combinations. The configuration of z = 6 mm, v = 500 mm/s and P = 800 W resulted in a remelted pool with 710 µm width and 242 µm length without major porosities, therefore being the largest stable pool amongst all parameters combinations. The resulting cellular microstructure had an interphase spacing of 0.93±0.17 µm, a decrease of about 14 times in relation to that of the substrate. The effects of LSR on the microhardness were remarkable, with the remelted pool presenting Vickers microhardness of 49±2 HV which corresponds to an increase of about 40% when compared to the original substrate.

Keywords: Laser surface remelting; Hypoeutectic Al-Fe alloy