Effect of Thermal Exposure on the Crystallographic Features and Surface Hardness of AA-7075-T6 Material

Abstract

Structural material AA-7075-T6, an aluminium-based alloy, was subjected to thermal exposure for 60 min in the temperature range 100–300 °C with an interval of 20 °C. Harris analysis of the XRD patterns of specimens showed that the un-exposed AA-7075-T6 material was texture free, but upon thermal exposure, it developed texture. The crystallite size and lattice strain of the specimens were evaluated by Williamson-Hall analysis of the XRD patterns. Thermal exposure in the temperature range 100‒200 °C had no noticeable effect on the surface hardness. However, it decreased rapidly with the increase in temperature from 200 to 300 °C. This behaviour was accounted for in terms of dislocation glide by Orowan mechanism in an atmosphere of semi-coherent ή precipitates (MgZn2) in the main matrix. Breakdown of Hall–Petch relation established that crystallite boundaries do not make any significant contribution to the surface hardness, but the resistance to glide dislocations is offered by the semi-coherent ή precipitates (MgZn2) present in the matrix.