Rapid Hot Extrusion Research Articles

Effects of Ca addition and rapid hot extrusion on the internal structure and dynamic precipitation of a novel CaMgSn ternary phase

A novel CaMgSn phase with unique internal structure-granular covering structure—has been observed and investigated in Mg–Sn–Zn–Ca extruded alloys. SEM, XRD and TEM confirm that the as-extruded alloy consists of α-Mg, separate Mg2Sn nanophase and rode-like CaMgSn ternary phase. It is also demonstrated that CaMgSn phase mainly contains Mg2Sn and Mg2Ca phases, and Mg2Sn nanoparticles are wrapped in Mg2Ca inside CaMgSn phases which bases on the dynamic precipitation mechanism. In addition, the orientation relationships among Mg, Mg2Sn and Mg2Ca have been identified.

Effect of tungsten content on microstructure and quasi-static tensile fracture characteristics of rapidly hot-extruded W–Ni–Fe alloys

Tungsten heavy alloys (WHAs) with three different compositions (90W–7Ni–3Fe, 93W–4.9Ni–2.1Fe and 95W–3.5Ni–1.5Fe, wt.%) were heavily deformed by one-pass rapid hot extrusion at 1100 °C with an extrusion speed of ~ 100 mm/s and an extrusion ratio of ~ 3.33:1. The influence of tungsten content on the microstructure and tensile fracture characteristics of the as-extruded alloys was investigated in detail. The results show that the tungsten particles in the as-extruded 95W have the largest shape factor compared to the as-extruded 90W and 93W alloys and this implies that the tungsten particles in the as-extruded 95W alloy were subjected to the heaviest plastic deformation. In addition, ultimate tensile strength (UTS) and hardness (HRC) are significantly improved after rapid hot extrusion. The as-extruded 95W alloy processes the highest strength (1455 MPa) and hardness (HRC40) but the lowest elongation (5%), followed by the as-extruded 93W (UTS1390MPa; HRC39; 7%) and 90W alloys (UTS1260MPa; HRC36; 10%). The fracture morphology shows the distinct fracture features between the as-sintered alloys and the as-extruded alloys. For the as-sintered alloys, the fracture modes are various while transgranular cleavage of tungsten particles is the main characteristic in the as-extruded alloy. Meanwhile, the fracture modes of the three as-extruded alloys vary slightly with the tungsten content. TEM bright field images indicate that many lath-like subgrains with the width of 150–500 nm are present in the three as-extruded alloys, particularly in the as-extruded 93W and 95W alloys. Furthermore, the dislocations are absent in the γ-(Ni, Fe) phase. This means that dynamic recovery–recrystallization process took place during rapid hot extrusion.

Microstructure and highly enhanced mechanical properties of fine-grained tungsten heavy alloy after one-pass rapid hot extrusion

One-pass rapid hot extrusion of fine-grained 93W–4.9Ni–2.1Fe–0.03Y (wt.%) alloy with an average grain size of ∼10 μm was performed at 1150 °C with an extrusion speed of ∼100 mm/s and an extrusion ratio of ∼3.33:1. Microstructure and mechanical properties of the as-extruded alloy were investigated. The results show that the tungsten particles of the as-extruded alloy are severely elongated along the extrusion direction and the aspect ratios of these elongated particles are 5–8. Three crystallographic textures {0 0 1}〈1 1 0〉, {1 1 1}〈1 1 0〉 and {1 1 0}〈1 1 0〉 arose after rapid hot extrusion and the total volume fraction of these texture components was approximately 30%. Many lath-shaped subgrains with a small misorientation and low density dislocations could be observed in tungsten phase and γ-(Ni, Fe) phase respectively. These microstructure characteristics indicate that slight dynamic recovery-recrystallization process occurred during rapid hot extrusion. In contrast to as-sintered alloy, the as-extruded alloy possessed much higher ultimate tensile strength and hardness (HRC) but a relatively lower ductility (1570 MPa vs. 995 MPa; HRC48 vs. HRC29 and 6.5% vs. 24%). In addition, the fracture morphology shows that the predominant failure mode for the as-extruded alloy is cleavage failure of the tungsten particles, while the ductile rupture of the γ-(Ni, Fe) phase that can be frequently observed in the as-sintered alloy nearly disappeared after rapid hot extrusion.