Experimental and modelling study of ultra-fine grained ZK60 magnesium alloy with simultaneously improved strength and ductility processed by parallel tubular channel angular pressing

Abstract

Ultrafine grained ZK60 magnesium (UFG–ZK60 Mg) tubes were successfully fabricated by a parallel tubular-channel angular pressing (PTCAP) process. The number of pass effects on the phase composition, microstructural features and mechanical properties were examined. Also, two types of Artificial Neural Network known as Radial Basis Function (RBF) and Multi-Layer Perceptron (MLP) were employed to accurately estimate mechanical behavior of the PTCAP-processed ZK60 Mg alloy. The results showed that all the processed tubes had more refined microstructure with ~ 7 to 0.9 µm grain sizes, which consist of an average crystallite size between 68 ± 8 and 51 ± 8 nm, compared to the as-received specimen with a mean grain size of ~ 90 µm. Similar XRD profiles were achieved following different PTCAP passes, however, some discrepancies were observed as the number of passes increased, which corroborated the structural changes during the PTCAP process. The microscopic observations also revealed the microstructural changes by increasing the PTCAP passes. The hardness of the processed tubes increased with the number of PTCAP passes, from 77 ± 2 HV for the unprocessed alloy to a maximum of 111 ± 2 HV at three PTCAP passes. The PTCAP process increased not only mechanical strength but also the ductility of the processed tubes, where the highest yield strength (sYS = 320 MPa), ultimate tensile strength (sUTS = 397 MPa) and elongation to failure (d = 14%) values were obtained at the second pass of PTCAP. However, with increasing number of PTCAP passes to three, d reached 4% and sYS and sUTS decreased by 31% and 11%, respectively. Findings from the neural based-predictive models indicated that both RBF and MLP can be employed for accurately estimating the mechanical properties of the PTCAP-processed ZK60 Mg alloy.