Effects of grain refinement on mechanical properties and microstructures of AZ31 alloy

Cerium was added in AZ31 alloy with the contents of 0.4%, 0.8% and 1.2% respectively to produce experimental alloys. The grain refinement of Ce in the as-cast and rolled AZ31 alloy were studied by using Polyvar-MET optical microscope with a VSM2000 quantitative analysis system, KYKY2000 SEM and Tecnai G2 20 TEM. And the mechanical properties of AZ31+Ce alloy were tested on a CSS–44100 testing system with computerized data acquisition. The results show that the cerium has a good grain refinement effect on the as-cast AZ31 alloy because cerium can build up a solute enriched zone rapidly during the solidification process. The dynamic recrystallization (DRX) grains less than 10 μm can be obtained in hot rolled AZ31+Ce alloy. A cold rolling deformation degree over than 20% and a following annealing at 400 °C for 1 h will lead to refine and uniform grains with the sizes of about 25 μm. The cerium can form dispersed and thermally stable Al4Ce phase that can prohibit the coarsening of grains in AZ31+Ce alloy during the hot rolling and annealing process.