Procedure for the production of thixotropic magnesium alloys

Abstract

Procedure for the production of a thixotropic magnesium alloy by adding a grain refiner combined with controlled, rapid solidification with subsequent heating to the two-phase area. It is preferable to use a solidification rate of >1.degree. C./s, more preferably >10.degree. C./s. It is essential that the solidification takes place at such a speed that growth of dendrites is avoided. Heating to the two-phase area is carried out rapidly in 1-30 minutes, preferably 2-5 minutes. By heating an alloy comprising 2-8 weight % Zn, 1.5-5 weight % RE, 0.2-0.8 weight Zr balanced with magnesium to a temperature in the two-phase area after casting, the structure will assume a form in which the .alpha.-phase is globular (RE=rare earth metal). The size of the spheres will be dependent on the temperature and the holding time at that temperature and they will be surrounded by a low-smelting matrix. It is preferable that the alloy has a grain size of not greater than <100 .mu.m, more preferably 50-100 .mu.m. A grain-refined magnesium alloy comprising 6-12 weight % A1, 0-4 weight % Zn and 0-0.3 weight % Mn also assumes thixotropic properties when heated to the two-phase area. Grain refiners such as Zr or carbon-based agents such as, for example, wax/fluorspar/carbon powder or calcium cyanamide can be used, depending on the alloy.