Computational design of additively manufacturable, cost-effective, high-strength aluminum alloys exploiting rapid solidification

Abstract

Aluminum (Al) alloys are widely used in aerospace and automotive industries as a result of their high strength-to-density ratio and cost-effectiveness, with their use at room temperature in housings and brackets. Although additive manufacturing (AM) facilitates the manufacturing of high-temperature aluminum alloys (200-400°C) to enable their potential use in intake fans and engine pistons, few alloying systems can sufficiently inhibit dislocation motions to achieve high strength, and their dislocation blockage features can hardly be retained at elevated temperatures. The high-demand service also requires reducing the material cost and CO2 emissions (net cost) without sacrificing mechanical performance. The two main blockage features for Al alloys are: the introduction of pinning sites that disrupt dislocation motions, generating tortuous paths; and interfaces that cause dislocation pileups and prevent plastic deformation. The mechanical design of the microstructure promotes an increase in the percentage of volume and a reduction in the length scale of these features to achieve higher strength. Here, we show that we can exploit rapid solidification in laser-based AM to introduce new pathways to achieve the mechanical design via precipitation of metastable phases that form at high fractions and with sub-micron length scale. Furthermore, with thermal aging, these phases transform into exceptional volumes of nanometer-scale pinning sites that are stable at high temperatures. We performed high-throughput calculated phase diagram (CALPHAD)-based integrated computational materials engineering (ICME) simulations along with inverse design using Bayesian optimization. We propose Al-Ni-Er-Zr-Y as a class of Al alloy that the cost/strength trade-off can be tailored by Er/Y ratio. Our high-temperature design has 95% strength of a benchmark printable Al alloy with 15% anticipated net cost savings. For room temperature use, by substituting Er with Y, in the first design, metastable phases can be exploited to achieve 3× room-temperature strengthening of the benchmark design with a 60% net cost reduction. The second design matches the strength of the benchmark alloy with 80% net cost savings.