Construction of extrusion limit diagram for AZ31 magnesium alloy by FE simulation

The maximum speed at which magnesium can be extruded is considerably slower than that of many common aluminium extrusion alloys. This affects both the economies of production and the final mechanical behaviour. The present work quantifies the limiting extrusion speeds and ratios of magnesium alloy AZ31 as a function of billet temperature. This is done by combining hot compression test results, FE simulations and extrusion trials. Hot working stress–strain curves displayed a distinct dynamic recrystallisation peak. These data were used as a “look-up” table for the FE simulations in which the cracking limit was assumed to occur when the surface temperature reaches the incipient melting point. The maximum extrusion ratio predicted using FE analysis dropped from 90 to 40 when the extrusion ram speed was raised from 5 to 50 mm/s. The predicted limits agree well with the occurrence of cracking in both a laboratory and a commercial extrusion trial.<br />