Architecture of high-strength aluminum\u2013matrix composites processed by a novel microcasting technique

Chenwei Shao,Zhefeng Zhang,Xuegang Wang,Shuo Zhao,Robert O Ritchie,Yankun Zhu

doi:10.1038/s41427-019-0174-2

Abstract

As important lightweight structural materials, cast aluminum alloys have been largely used in the transportation and aerospace industries. In general, Al–Si-based alloys comprise more than 90% of all castings due to their excellent castability and corrosion resistance. However, even though various reinforcements have been introduced, the strength of these alloys is not that high, which severely limits their use for certain high-performance applications. Here, we report on a new strategy and technology to reinforce Al–Si alloys to increase their yield strength into the ~400–660 MPa range, a level that is 29–113% higher than that of all current cast Al–Si alloys, laboratory or commercial, and comparable to that of many high-strength steels but with ~40% lower density. By introducing continuous Ti–6Al–4V reinforcements into the Al–Si matrix through a novel microcasting process, the yield strength of the resulting alloy can be enhanced to between 4 and 6 times higher than that of the pure Al–Si alloy. The extraordinary reinforcing effect originates from the occurrence of multiscale strengthening mechanisms, including macroscale compound strengthening (the rule of mixtures amended by crack arrest mechanism), mesoscale strain-gradient strengthening, and microscale interface-affected-zone and nanoparticle strengthening. The core principle of our material design is to make all components of the composite fully participate in plastic (compatible) deformation, and thus, continuous reinforcements, instead of discrete reinforced structures (e.g., particles, whiskers, and short fibers), were introduced into the Al–Si alloy. Combined with 3-D printing technology, the present microcasting process can realize strengthening at the designed position by architecting specific reinforcements in the matrix.

Highlights

Aluminum–matrix composites (AMCs) are attractive and viable candidates for many military, aerospace, and automobile applications[1] due to their light weight and high performance compared to that of many conventional casting metals and alloys
Inspired by the idea of introducing strong continuous reinforcements into a matrix to significantly enhance the strength, we report on a novel method, the microcasting process, to reinforce a commercially cast aluminum alloy by introducing a titanium-alloy strut in the material using a low-cost, high-efficiency process
All interfaces between the Al/Ti phase were removed by the formation of the Al3Ti intermetallic phase, which is formed by the diffusion of titanium atoms from the reinforcement to the matrix when the temperature exceeds the melting point of aluminum[19,20]

Summary

Introduction

Aluminum–matrix composites (AMCs) are attractive and viable candidates for many military, aerospace, and automobile applications[1] due to their light weight and high performance compared to that of many conventional casting metals and alloys. AMCs with different types of reinforcements, such as particles[2], whiskers[3], fibers,[4] and sheets[5], have been produced to permit such composite alloys to be utilized in many practical applications[1,6,7]. The basic reason for this situation lies in the fact that most reinforcements are much harder and stronger than the aluminum matrix so that strengthening is mainly accomplished by the reinforcement restricting the deformation of the aluminum matrix.

Methods

Results

Conclusion