Comparison of the Mechanical Properties and Forming Behavior of Two Texture-Weakened Mg-Sheet Alloys Produced by Twin Roll Casting

Abstract

The influence of rolling and annealing on the resulting mechanical properties and forming behavior of Mg-Zn-RE and Mg-Zn-Ca alloys produced via twin roll casting is investigated. After hot rolling followed by an annealing treatment, both alloys develop a fine-grained microstructure with average grain sizes <10 µm. A distinctive development of a texture with a pronounced split of the basal poles in the transverse direction, so called TDsplit, is observed in both alloys during the annealing. Due to the fine microstructure and weak texture, which enhances the activation of basal <a> slip, both alloys show large ductility with fracture strain higher than 30%. However, due to the TD-split texture, a high asymmetry of the yield stress is observed, where the yield stress in rolling direction is significantly higher than the yield stress along 45 • and the transverse direction. Both alloys show high stretch formability at room temperature with Erichsen index around 7. Despite a low planar anisotropy and high stretch formability, the Mg-Zn-RE alloy shows undesirable earing behavior, while the Mg-Zn-Ca alloy fractures during warm deep drawing. Moreover, the deep drawing operation using the as-rolled sheet of Mg-Zn-RE alloy can be successfully done. It is observed that the earing behavior can be effectively reduced by deviating from the TD-split texture. In this regard, cold rolling was explored to reduce the anisotropy of the ductile and formable alloy.

Lean Wrought Magnesium Alloys

“…As the deformation behavior and the texture development are intrinsically linked, it is not surprising that extensive studies are being conducted regarding this aspect. Next to process adaptations [ 13 ], e.g., cross rolling, the alloy customization by (micro-) alloying with, for example, REE or Ca, is an accepted practice for texture reduction and enhanced forming behavior [ 16 , 29 , 30 , 31 , 32 ]. In particular, the combination of Zn and Ca is known to improve the forming behavior of various Mg alloys.…”

“…value of ~7 mm was reached, and industrially relevant components could be formed at temperatures of 160 C. In ref. [ 32 ], this ZXK alloy was compared to Mg-1.8Zn-0.1Nd-0.1Ce-0.05La-0.2Y material, which showed comparable I.E. values at RT.…”

“…In general, the ZEW sheets featured higher strength and increased ductility compared to the ZXK alloy, which, on the other hand, exhibited reduced planar anisotropy. In the forming investigations (Erichsen testing and deep drawing of cups), the ZEW sheets showed better overall performance under all conditions and temperatures tested (up to 200 C), while the ZXK material failed due to crack initiation at the coarse MgCa particles [ 32 ].…”

“…The combination of Zn and REE (sometimes refined by Zr additions ) is an often-chosen alloying route, known to produce alloys with good forming performances. Some of the works [ 32 , 83 ] investigating these alloys were already mentioned in Section 4.2 .…”

Alloying and Processing Effects on the Microstructure, Mechanical Properties, and Degradation Behavior of Extruded Magnesium Alloys Containing Calcium, Cerium, or Silver

“…Calcium (Ca) shows a strong influence on the texture development during rolling or extrusion [24,25], especially leading to weaker textures without a strong alignment of basal planes. Such textures are known to enable improved ductility and also lower anisotropic mechanical behavior [26]. As the most abundant mineral in the body, Ca is predominantly found in bone, and the release of Ca ions regulates the activation of osteoblasts and osteoclasts to facilitate bone regeneration in vitro [27], but also in vivo [28].…”