Thermodynamic Modelling on the Mutual Effect of Copper, Manganese and Iron Addition in Al-Si-Cu For Semisolid Processing

Semisolid metal (SSM) processing or Thixoforming is a new method for forming alloys in the semisolid state to near net shaped products. All the alloys which have been used to date for thixoforming were developed originally for either casting or forging operations. Thus, there is a lack of specific alloys for semi solid processing that present good fluidity, low viscosity and small grain size. Thermodynamic calculation software, such as Java-based Material Properties (JMatPro), provides a tool for predicting thixoformability of aluminium alloys. Here, the effects of compositional variations, in particular the effect of copper, manganese and iron additions on the thixoformability of alloy A319 have been investigated. This software was used to determine the processing temperature at 0.4 fraction liquid, working window temperature, fraction liquid sensitivity, solidification range and phase diagram during semisolid processing. The alloys modelled were divided into two groups according to their copper, manganese and iron contents. The working window temperatures (∆T0.3/0.5) for alloys in all two groups were enlarged at the range of 8°C to 14°C while the slope of the fraction liquid versus temperature curves at 0.4 fraction liquid become less steep from 0.014°C-1 to 0.010 C-1. The processing temperatures of modified alloys at 0.4 fraction liquid have decreased from around 558°C to 550°C and this would benefit the thixoformability of the selected material. Phase diagram was used to show the location of the intermetallic phases (i.e. Al5Cu2MG8Si6, α-Al(Fe,Mn)Si and Al2Cu) that dissolve in the semisolid zone. The results indicate the suitability of these modified alloys as a potential material for semisolid processing.