Effect of Heat Treatment Conditions on Mechanical Properties of Die-Casting Al–Si–Cu–xLa Alloys

TL;DR

Adding lanthanum to an aluminum alloy improves its hardness and corrosion resistance when treated with specific heat conditions.

Contribution

The study demonstrates that 0.5 wt.% La addition combined with optimal heat treatment significantly enhances mechanical and corrosion properties of Al–Si–Cu alloys.

Findings

0.5 wt.% La addition refines α-Al grains and increases hardness via the Hall–Petch mechanism.

Alloys with 0.5 wt.% La show best corrosion resistance due to LaCu2Al4Si intermetallic formation.

Solution treatment at 500 °C or higher and 2 h aging optimize mechanical performance.

Abstract

In this study, lanthanum (La), a rare earth element, was added at concentrations of 0.25 wt.%, 0.5 wt.%, and 0.75 wt.% to an Al–10%Si–2%Cu-based alloy prepared by die casting. The effects of solution and aging heat treatment conditions on the mechanical properties and corrosion resistance were investigated. Microstructural changes, hardness, and corrosion behavior were analyzed as functions of La content and heat treatment parameters. The optimal hardness was achieved at a solution treatment temperature of 500 °C or higher and an aging time of 2 h. In particular, the addition of 0.5 wt.% La led to significant refinement of the α-Al grains, enhancing hardness through the Hall–Petch strengthening mechanism. Furthermore, the combined effects of aging treatment and La addition promoted the formation of a fine, uniform microstructure and stable dispersion of precipitates, resulting in improved mechanical performance. Electrochemical polarization tests revealed that the alloy containing 0.5 wt.% La exhibited the best corrosion resistance. This enhancement was attributed to the formation of the LaCu2Al4Si intermetallic compound, which has a lower electrochemical potential than the Al2Cu phase, thereby reducing corrosion susceptibility within the microstructure.

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