Effect of Al-5Ti-C Master Alloy on the Microstructure and Mechanical Properties of Hypereutectic Al-20%Si Alloy.

Tiandong Xia,Yangtao Xu,Wenjun Zhao,Wanwu Ding

doi:10.3390/ma7021188

Abstract

Al–5Ti–C master alloy was prepared and used to modify hypereutectic Al–20%Si alloy. The microstructure evolution and mechanical properties of hypereutectic Al–20%Si alloy with Al–5Ti–C master alloy additions (0, 0.4, 0.6, 1.0, 1.6 and 2.0 wt%) were investigated. The results show that, Al–5Ti–C master alloy (0.6 wt%, 10 min) can significantly refine both eutectic and primary Si of hypereutectic Al–20%Si alloy. The morphology of the primary Si crystals was significantly refined from a coarse polygonal and star-like shape to a fine polyhedral shape and the grain size of the primary Si was refined from roughly 90–120 μm to 20–50 μm. The eutectic Si phases were modified from a coarse platelet-like/needle-like structure to a fine fibrous structure with discrete particles. The Al–5Ti–C master alloy (0.6 wt%, 30 min) still has a good refinement effect. The ultimate tensile strength (UTS), elongation (El) and Brinell hardness (HB) of Al–20%Si alloy modified by the Al–5Ti–C master alloy (0.6 wt%, 10 min) increased by roughly 65%, 70% and 51%, respectively, due to decreasing the size and changing the morphology on the primary and eutectic Si crystals. The change in mechanical properties corresponds to evolution of the microstructure.

Highlights

Hypereutectic Al–Si alloys have been widely investigated because of their excellent properties, which include excellent wear and corrosion resistance, high temperature strength, low coefficient of thermal expansion, good cast performance, and high specific strength [1,2,3]
The results show that 0.6% Al–5Ti–C alloy cannot only effectively decrease the size of primary Si and eutectic Si crystals in hypereutectic Al–20%Si alloy, but it can change the morphology of primary Si and eutectic Si crystals
Microstructural survey of samples was conducted with optical microscopy (OM) and scanning electron microscopy (SEM) after preparing samples according to standard metallographic procedures, which were etched using Keller’s reagent (2.5 mL HNO3, 1.5 mL HCl, 1 mL HF, and 95 mL H2O).The unmodified ingot was obtained under the same procedure without adding Al–5Ti–C master alloy

Summary

Introduction

Hypereutectic Al–Si alloys have been widely investigated because of their excellent properties, which include excellent wear and corrosion resistance, high temperature strength, low coefficient of thermal expansion, good cast performance, and high specific strength [1,2,3]. In order to refine the primary silicon, many methods have been carried out, such as high-pressure casting, the rapid solidification technique [9], and melt overheating treatment [10,11,12] These processes are complex and difficult to control. Phosphor is the most effective refinement element of primary Si in hypereutectic Al–Si alloy [13,14]. Attention has been given to the complex modification of primary and eutectic Si in order to significantly enhance the mechanical properties of hypereutectic Al–Si alloys. Al–Ti–C–Sr master alloys and reported that satisfactory grain refining and modifying effects were obtained by the addition of Al–Ti–C–Sr alloys (0.5 wt%) to the A356 alloy. Little has been reported on the microstructure and mechanical properties of hypereutectic Al–20%Si alloy with the addition of Al–Ti–C master alloy. The mechanical properties and hardness of the hypereutectic Al–20%Si alloy were studied

Microstructures of Al–5Ti–C Alloy

Analyses of Mechanical Properties

Experimental Section

Conclusions