Twin-Roll Cast Wrought Magnesium Alloys with Improved Rollability and Formability

Wrought magnesium alloys have a good set of engineering properties that make them ideal candidates for use in the electronic and automotive industries. They include light weight, high specific strength, stiffness, good damping characteristics, excellent shielding capability against electromagnetic interference and effective heat dissipation. Their wide use, however, is limited by the high cost associated with the production of sheets. In conventional magnesium sheet production, alloy slabs of 0.3 m x 1 m x 2 m produced by direct chill (DC) casting are homogenised for several hours followed by continuous hot rolling to a final thickness of 5-6 mm. This sheet is then annealed before each pass of 5-20% reduction until required thickness is achieved. This process is costly and time consuming. With the advent of twin-roll casting (TRC) of magnesium alloys coils, (approximately 100 m in length) 600 mm wide x 3 mm thickness, can be produced from the melt, significantly reducing the cost of sheet production. In TRC cooling rates in the range of 500 to several thousands of degrees per second are achieved leading to refined grain size and increased solid solubility resulting in significant improvements in the mechanical properties of the finished sheets. In this presentation the rollability and formability of twin-roll cast wrought magnesium alloys containing zinc and rare-earth elements discussed. It will be shown that a significant reduction in the number of rolling passes can be achieved with this alloys compared to commercially available magnesium alloy AZ31B. The rolling temperatures and forming temperatures are also lower for these alloys making it much easier to use in present day industrial set-up.