Texture Randomization of AZ31 Magnesium Alloy Sheets for Improving the Cold Formability by a Combination of Rolling and High-Temperature Annealing

摘要

To improve the cold formability of AZ31 magnesium alloy sheets, we investigate texture control by rolling and annealing. The texture ideal for forming close to random orientation was obtained by annealing at 773 K before and after isothermal rolling at 298-573 K. For the randomizing process, such a high temperature in pre-annealing was essential, whereas a slightly lower temperature was acceptable for final annealing, assuming a sufficiently long annealing time. The randomized sheet could be obtained in a wide range of rolling temperatures and reductions. It could also be produced easily with a standard mill without roll heating. The microstructure of the randomized sheet consisted of relatively homogeneous grains 25-30 μm large on average. In a 90 degree V-bending test, a well randomized sheet could be bent without cracking with a minimum bending radius per thickness R/t = 1.4, which was about half of that in commercial AZ31D-O sheets, in spite of manganese content of over 0.6%.