Characterization of the Microstructure and Rheological Behavior of Al-4wt%Si-2.5wt%Cu Alloy Produced by Direct Chill Casting and Electromagnetic Stirring

Abstract

This work involved an evaluation of a Al-4wt%Si-2.5wtCu alloy to be used as raw materials in the thixoforming process. The alloy was produced by direct casting under electromagnetic stirring to obtain ingots of 250 mm length and 30 mm diameter. The alloy was analyzed to determine their morphology and rheological behavior in the semi-solid range. The tests included characterization of the microstructural evolution by subjecting them to re-heating treatment in two conditions of solid fractions, 45% and 60%, for 0, 30, 90 and 210 s. A compression testing device designed specifically to evaluate semi-solid materials was used to determine the rheological behavior, and the tests were performed at the same heating rate and hold times to determine the apparent viscosity. The use of electromagnetic stirring to produce the raw material was effective in producing alloy with very small grain/primary particle sizes (80 up to 120 µm). Based on the morphological evolution in the semi-solid state, the alloy showed only minor variations in grain/primary particle size and surface factor (SF) as a function of the different globularization heat treatment times, suggesting that all these alloys are suitable for production. The Al-4.0wt%Si-2.5wt%Cu alloy with 45% solid fraction presented apparent viscosity about 1.5 x106 Pa.s.