Superior ductility and strength enhancement of ZK60 magnesium sheets processed by a combination of repeated upsetting and forward extrusion

Abstract

This research work is concerned with creation of ZK60 Mg sheets by various combinations of the repeated upsetting (RU) and forward extrusion (Ex) operations. The RU process was conducted with different passes and at 250 ℃, whereas the subsequent forward extrusion was performed at 220 ℃. Complementary tensile tests together with fractography, and microstructural and textural studies were carried out in order to investigate the influence of the process types and conditions on the material properties of the sheet products. It was found that combination of the RU and Ex operations could result in ductile ZK60 sheets with improved strength and strain hardening capacity. The maximum elongation was achieved after 3 passes of RU followed by Ex process. This processing route also resulted in balanced ultimate strengths in both extrusion and transverse directions with almost the highest strain hardening capacity. The effects of RU number of passes and forward extrusion process on the microstructures, textures, mechanical properties and the fracture of the ZK60 sheets were also investigated and, based on the experimental findings obtained; several important conclusions were drawn and explained in this article.

Microstructure, texture and mechanical behavior characterization of hot forged cast ZK60 magnesium alloy

“…The results of this study and of a similar upsetting Ref. [37] (also shown in Table 2) demonstrate that higher ductility is always achieved after forging, compared to the ductility of as-cast or asextruded materials. It is evident from Fig.…”

“…µm) with elongated grains (~1 mm long and ~50 µm thick) [33], which significantly improved the ductility and tensile strength [34], leading to the improvement of low cycle and high cycle fatigue properties [35,36]. More recently, researchers reported achieving superior ductility and strength enhancement of ZK60 Mg alloy sheets by a combination of repeated upsetting and forward extrusion [37]. Accordingly, most of the machine parts in manufacturing industries are forged in one pass instead of multiple passes.…”

Hot Rolling of ZK60 Magnesium Alloy with Isotropic Tensile Properties from Tubing Made by Shear Assisted Processing and Extrusion (ShAPE)

“…Typically, in ZK60, it has been observed that the yield strength along the rolling direction is approximately 50% lesser than in transverse direction. The strength of the plates at both 68% and 93% reduction showed higher values of strength in both transverse and longitudinal directions with no anisotropy as compared to what has been reported in the literature [42]. Additional rolling appears to lead to an overall reduction in tensile properties and an increase in the apparent anisotropy.…”

“…Typically, in ZK60, it has been observed that the yield strength along the rolling direction is approximately 50% lesser than in transverse direction. The strength of the plates at both 68% and 93% reduction showed higher values of strength in both transverse and longitudinal directions with no anisotropy as compared to what has been reported in the literature [42]. It is important to mention, for example, that while the ZK60 sheets in this work were rolled immediately after heating, the sheets were not held at an elevated temperature for rolling, and the rollers themselves were not heated.…”

Bimodal grain microstructure development during hot compression of a cast-homogenized Mg-Zn-Zr alloy

“…Wrought ZK60 alloys possess the best combination of room temperature strength and ductility among the available wrought Mg alloys [12]. Moreover, this alloy is known to be a suitable alloy for hot deformation and fabrication of wrought products [13][14][15][16][17][18][19][20][21][22] where DRX dominates microstructural evolution during hot deformation [23][24][25][26][27]. However, various studies have reported a bimodal grain microstructure consisting of fine recrystallized grains and elongated unrecrystallized ones, which resulted from hot deformation of ZK60 alloy due to partial DRX [25][26][27][28][29].…”