Precipitation Studies of Undeformed and ECAP-Deformed Al-4%Cu Alloys: Effects on Microstructure and Tensile Properties

Abstract

The present study is an assessment of the effects of precipitation heat treatments on tensile behaviour, work hardening (WH) characteristics and microstructural evolution of an Al-4%Cu alloy deformed by equal channel angular pressing (ECAP). Two ageing temperatures were employed (170 and 100oC) and their effect on strength and WH behaviour was compared with that exerted on the same alloy, but in two different initial conditions: quenched from solution temperature and slowly cooled before anneal. Grain and precipitate sizes of samples deformed by one and four ECAP passes and heat treated as described were measured employing transmission electron microscopy (TEM). It was concluded that the lower ageing temperature gives the best combination of strength and ductility, a high WH rate and, possibly, the smaller grain and precipitate sizes. The relative participation of the various hardening mechanisms to total strength was estimated from tensile tests and hardness measurements.

A Short Summary of Present Knowledge and some Experimental Observations on the Ductility of Sub-Microcrystalline Aluminium Alloys

“…Altogether, two different approaches can be recognized: (i) alloys with pre-existing precipitates are submitted to SPD; (ii) precipitation heat treatment follows SPD. In the former, particles are fractured by the intense shear, forming a finer dispersion, and in many investigations dissolution of these debris is mentioned [55,19]. For instance, natural aging, followed by ECAP and artificial aging were applied to a AlZnMg alloy [56].…”

“…While HPT is still in need of a better understanding of the relationships between microstructure and operational parameters, such as pressure and number of turns, the ECAP process has been intensively studied and some examples of the main research topics are: the determination of deformation textures and the concurrent microstructural evolution [11,12,13]; the influence of interpass billet rotation on microstructural evolution and homogeneity [14,15], the effect of recrystallization or recovery anneal on microstructure, mechanical properties, texture and microstructural stability [16,17,7], and finally how SPD affects precipitation [18,19,20].…”