Structural, electrical, and mechanical characterization of Al 5086 alloy irradiated with 248 nm–20 ns KrF excimer laser

Abstract

Williamson-Hall analysis of XRD patterns of Al 5086 alloy specimens (10 mm × 10 mm × 6 mm) irradiated with 100–500 KrF excimer laser pulses in air (1 bar) as well as in vacuum (10−3 mbar) was done to evaluate structural changes on laser irradiation. Both crystallite size (30 nm–99 nm) and lattice strain (0.00043–0.00241) were found, in general, to increase with the number of laser shots first rapidly up to 200 and later on rather slowly. Also, for a given number of laser shots, the crystallite size of the specimen laser-irradiated in vacuum was higher than that of the specimens laser-irradiated in air. Harris analysis of XRD patterns revealed that the most preferentially oriented plane was (200) with texture coefficient in the range 2.359–2.982. Electrical resistivity of the specimens was measured by four-point probe technique. It was found to increase with the number of laser shots up to 200, and later on decreases monotonically. However, for a given number of laser shots, its value was higher for the specimen laser-irradiated in air than that for the specimen laser-irradiated in vacuum. On plotting combined surface hardness data for un-irradiated and laser-irradiated specimens in air as well as in vacuum as a function of inverse square-root of crystallite size, a cross over from classical Hall-Petch relation (99 nm–55 nm) to inverse Hall-Petch relation (55 nm–30 nm) occurred at about 55 nm. This is true not only for the surface hardness but also for the hardness measured at 0.5 and 1.0 mm depth below the specimen surface. The intensity of laser-hardening effect gradually diminishes as one goes down from the uniformly laser-irradiated specimen surface to a depth of 3.0 mm below it. The relationship between electrical resistivity and surface hardness was linear.