On microstructure and room-/high-temperature properties of an Al2O3/Al-Cu-Mn composite

Abstract

An Al2O3/Al-Cu-Mn composite was fabricated using a combination of ball milling and liquid-solid reaction, with a nominal composition of Al-4Cu-0.5Mn-2.8γ-Al2O3. The composite contains reinforcement particles, including nano-sized θ’ and T(Al20Cu2Mn3) particles after T6 heat treatment, as well as in-situ synthesized nano-sized γ-Al2O3 particles. Tensile tests of the Al-4Cu-0.5Mn-2.8γ-Al2O3 composite and the Al-4Cu-0.5Mn base alloy after T6 treatment were carried out at room temperature and elevated temperatures (200 °C, 300 °C, and 400 °C). Compared with the base alloy, the yield strength of the Al-4Cu-0.5Mn-2.8γ-Al2O3 composite after T6 treatment increases significantly from 187 MPa to 263 MPa at room temperature. Simultaneously, at elevated temperatures, the yield strength is also enhanced, with a yield strength of 52 MPa at 400 °C for this composite. The in-situ fabricated γ-Al2O3 particles, mainly distributed along the grain boundaries, are supposed to play the main strengthening role, especially at high temperatures. This work acts as a reference for designing composites for high-temperature applications.

1. Introduction

Al-Cu-Mn-based alloys are widely used in aerospace and automotive industries due to their lightweight and high strength [1, 2]. In recent years, extensive research has focused on utilizing elements such as Zr, Sc, Er, and Gd to further improve the tensile strength of the alloys [3, 4]. However, the concept by increasing alloying element content to enhance the tensile properties of Al-Cu-Mn-based alloys is limited, as the alloys are highly susceptible to casting defects during solidification when the element content is high to some extent, e.g., porosity, hot tearing, and segregation, which can significantly degrade the mechanical properties of the alloys [5].

Except for traditional alloying theory, the development of aluminum matrix composites (AMCs) has attracted much attention due to their typically low density, high strength, and excellent high-temperature (HT) properties [6, 7]. The desired material is achieved by controlling the type, morphology characteristics, size, and distribution of the reinforcing particles in the matrix. Currently, AMCs are mainly fabricated by either ex-situ or in-situ methods. The ex-situ methods, such as the casting method (e.g., melt-stirring [8] and squeeze casting [9]), are commonly used to prepare the AMCs. However, the problem of poor wettability at the interface between the Al matrix and reinforcing particles, results in a susceptibility of the interface to contamination [10, 11]. In contrast, in-situ methods exhibit obvious advantages in overcoming these drawbacks [12]. The in-situ methods are mainly based on the in-situ synthesis of ceramic particles and related intermetallic compounds as reinforcements through aluminum thermal substitution reaction between Al and precursors [13]. Reinforcements generated via in-situ methods are characterized by their non-pollution interfaces with the matrix and excellent high-temperature stability [14]. Thus, in-situ methods have received extensive attention and development in recent years, with self-propagating synthesis [15] and liquid-solid reaction [16, 17] being commonly utilized techniques.