Abstract
Effect of heat treatment and isothermal holding has been investigated on the microstructure and degree of globularity of Al–Mg2Si composites. Different contents of reinforcement, 15, 20, and 25% have been used in this study. Isothermal holding experiments were conducted at 585 °C for 140 min. Results showed that, upon heat treatment, grain size of dendrites was reduced while the degree of nodularity was increased. Results of nodularity were obtained using an image-analyzing software which gives the distribution of radius of curvature for different phases of particles. According to the results, in contrast to Al–15 and 25% Mg2Si, isothermal holding significantly influenced the microstructure of Al–20% Mg2Si composites. Two companion mechanisms have been proposed for the generation of globular grains. SEM investigations were also employed to confirm the optical observations.
Highlights
Superior mechanical properties, as well as increased possibility to control the production process have been the main challenge with which manufacturing of engineering materials is faced
It is clear from the phase diagram (Figure 1) that the compositions of all samples are located in the hyper section of the diagram. This means that the microstructure is consisted of coarse primary Mg2Si particles in a matrix of α-Al and pseudoeutectic cells
The microstructure of the sample with 15% of Mg2Si prior to the heat treatment (Figure 5(a)) reveals a nondendritic and coarse morphology for reinforcement particles, but the dendritic and coarse morphology is obvious for the samples with 20 and 25% Mg2Si (Figures 5(c) and 5(e))
Summary
As well as increased possibility to control the production process have been the main challenge with which manufacturing of engineering materials is faced. Semisolid processing is claimed to be one of the best approaches which can fulfill such properties. The aim of the semisolid processing is to achieve a fine globular structure. It is clear that controlling the microstructure of semisolid material is of great importance [1,2,3]. Possessing a fine globular (nondendritic) microstructure which can be obtained through semisolid-forming processes yields superior advantages over conventional casting and solidforming methods among which one can mention high quality components capable of full-heat treatment to maximize properties, reduction of macrosegregation, solidification shrinkage, and forming temperature [1,2,3,4]
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