Analysis of defects in a twin roll cast Mg‐Y‐Zn magnesium alloy

Abstract

Twin roll casting (TRC) enables the production of magnesium strips in an economic manner. TRC has enormous potential for the production of thin strip material from magnesium alloys. However, a range of defects may arise during casting. Internal and surface defects also influence the final properties of TRC strips. In this work, the magnesium alloy Mg‐6.8Y‐2.5Zn‐0.4Zr (WZ73) containing long‐period stacking ordered (LPSO) structures was twin roll cast with different process parameters, and the defects that arose were investigated. In particular, defects such as surface bleeds, center‐line segregations and deformation segregations in the mid‐thickness of the strip were observed and analyzed with regard to the TRC parameters applied. The latter may have developed due to the solidification of solute‐rich liquid in the center of the strip. X‐ray diffraction analysis was carried out to determine the phase compositions within the casting defects. A (Mg,Zn)3Y phase was found to precipitate in a blocky or lamellar shape within large, plate‐like LPSO phases. Wavy lines resulting from high specific rolling forces can be avoided if specific rolling force does not exceed a value of 8 kN/mm. Casting speed of 1.5 m/min has proven to be favorable to prevent the occurrence of center‐line segregation.

Twin-Roll-Casting Technology for the Magnesium Strip

“…For example, when using rare earth alloys, the TRC process enables the production of sheets with high strengths. Important alloys in this regard are WE43 [9] and, most recently, WZ73 [10,11]. In addition, investigations were carried out with the calcium-containing alloys MX21 and ZAX210 [12][13][14].…”