Characterization of heat treatment-driven microstructural evolution, mechanical properties and electrochemical behavior of direct powder forged Al–10Si–0.3Mg alloy

Abstract

This study investigated the effects of direct aging (DA), solution treatment (ST), and ST followed by DA (T6) on the microstructural, mechanical, and corrosion properties of direct powder forged Al–10Si–0.3Mg alloy specimens. Microstructural analyses conducted using optical microscopy, scanning electron microscopy, and electron backscatter diffraction revealed that among DA specimens, direct aging at 200°C (DA-2) exhibited significantly enhanced silicon (Si) particle distribution uniformity and minimal interparticle boundaries owing to increased diffusion bonding; ST specimens exhibited partial Si dissolution, higher porosity, and retained the interparticle boundaries; and T6 specimens exhibited improved microstructural uniformity and enhanced Si precipitation. Furthermore, mechanical property evaluations indicated that T6 treatment comprising ST at 500°C for 180 min followed by DA at 200°C for 360 min resulted in the highest tensile strength (207.15 MPa) and elongation (5.02%), followed closely by DA at 200°C for 360 min (203.13 MPa and 4.39%). These improvements were attributed to the lower residual stress, higher diffusion distances, and well-dispersed Si particles induced by DA-2 treatment. Corrosion analyses conducted using cyclic polarization and impedance spectroscopy indicated varied electrochemical responses, with DA-2 resulting in the lowest corrosion current and highest impedance, and ST resulting in the lowest corrosion resistance. Overall, DA at 200°C for 360 min was the most effective heat treatment, offering the optimal balance between mechanical and corrosion-resistance properties.

1. Introduction

Aluminum alloys are essential in the aerospace, automotive, and marine industries owing to their light weight, excellent strength-to-weight ratio, corrosion resistance, and thermal stability. Among these, Al–Si–Mg alloys—especially AlSi10Mg—have gained prominence owing to their ability to be easily age-hardened and cast as well as their excellent performance [1–2].

The AlSi10Mg alloy is widely used in traditional manufacturing processes, such as casting and high-pressure diecasting, as well as more advanced processes, such as selective laser melting (SLM) and direct powder forging (DPF) [3–8]. Casting is cost-effective and facilitates large-scale production, but its use of slower cooling rates (~10²°C·s⁻¹) can produce coarse Si particles and common defects, such as porosity and inclusions, that reduce mechanical performance [9–11]. These drawbacks have been addressed by newer manufacturing technologies, such as SLM, that provide rapid cooling rates (up to 10⁶–10⁸°C·s⁻¹), enabling the formation of fine cellular dendritic Si networks on the Al matrix. However, parts fabricated using SLM often exhibit issues such as high residual stress, microstructural anisotropy, porosity, and size limitations [12–13].

Researchers such as Dwivedi et al. [7] have attempted to address these issues through the application of DPF to produce Al–10Si–0.3Mg components. The DPF technique combines the benefits of powder metallurgy and forging to enable near-full densification as well as improved distribution of Si particles and stronger bonds between grains than either method in isolation. As a result, DPF is especially valuable for producing parts at scale for critical sectors such as transportation and aerospace. However, forging can introduce residual stresses and microstructural inconsistencies that affect the strength and long-term durability of a material, highlighting the value of subsequent heat treatment. Kuang et al. [14] demonstrated that thermal exposure significantly influences the microstructure and mechanical properties of Al alloys. Previous studies have shown that thermal treatment significantly influences solute redistribution and phase transformation kinetics in metallic systems [15–16], thereby emphasizing the importance of optimized thermal processing.