Enhancing the Mechanical Properties of ADC12 Aluminum Alloy via T6 Heat Treatment

ADC12 aluminum alloy is a widely used commercial material, known for its exceptional corrosion resistance, heat resistance, and impact strength. It is commonly employed in the production of high-quality components and is found in applications such as automobiles, electrical appliances, pneumatic systems, and pressure vessels. High-pressure die casting, also known as liquid die forging, is a process that combines elements of both casting and forging. In this molding process, molten metal is injected into a metal mold under high mechanical pressure, causing it to solidify and undergo plastic deformation. The key characteristic of this process is the application of pressure during solidification, which facilitates shrinkage compensation and induces controlled plastic deformation. Currently, there is a growing demand for high-strength, high-quality structural components for new energy vehicles, which necessitate the use of die casting for manufacturing.
 
Heat treatment can modify the microstructure of ADC12 aluminum alloy, thereby affecting its mechanical properties. Xingjie Li et al. studied the impact of heat treatment on the structure and properties of ADC12 aluminum alloy to determine the optimal heat treatment parameters. The results showed that, after solution treatment at 520°C for 5 hours and artificial aging at 170°C for 10 hours, the alloy exhibited a room temperature tensile strength of 283MPa and an elongation of 2.52%.

Zeng et al. investigated the effect of the aging process on the hardness of ADC12 aluminum alloy die castings. The results indicated a significant increase in hardness of approximately 15% when the castings were aged at 175°C for 8 hours and air-cooled. Current research primarily focuses on the impact of various heat treatments on the mechanical properties of die-cast aluminum alloys; however, there is limited research on the T6 heat treatment of high-pressure die-cast aluminum alloys. This study examines the influence of different T6 heat treatment processes on the microstructure and properties of high-pressure die-cast ADC12 aluminum alloy.
 

The experimental materials consist of die-cast components made from commercial ADC12 aluminum alloy, manufactured by high-pressure die casting. The alloy has a liquefaction temperature of 660°C, and its chemical composition was analyzed using an iCAP7400 DUO optical emission spectrometer (OES), as shown in Table 1.
 
Table 1 Chemical composition of the ADC12 aluminum alloy

 
The ADC12 aluminum ingot was heated to 800°C in a graphite crucible and held at this temperature for 40 minutes. Once the alloy was completely molten, it was degassed using argon (Ar) and refined for 10 minutes. When the melt cooled to the target pouring temperature of 680°C, it was immediately injected into the injection sleeve of a high-pressure die-casting machine, with an injection speed of 0.5 m/s and an injection pressure of 90MPa to form the die casting part.

To improve the performance of the die casting part, it was subjected to T6 heat treatment, consisting of solution treatment followed by artificial aging. Solution treatment is a heat treatment process in which the aluminum alloy is heated to the single-phase region, held at that temperature, and then rapidly cooled to form a supersaturated solid solution. The aging process involves either keeping the supersaturated solid solution at room temperature or heating it to a specific temperature for a defined period. Over time, the strength and hardness of the alloy increase, while its plasticity and toughness decrease. The time interval between solution treatment and artificial aging is controlled to within 15 minutes. The T6 heat treatment process applied to the samples for microstructural observation and phase analysis in this study involved a 510°C solution treatment for 1 hour, followed by artificial aging at 200°C for 6 hours. The specific process flow is shown in Figure 1.
 

Figure 1 Process flow of the ADC12 aluminum alloy die casting preparation and heat treatment

 
The die castings, both before and after heat treatment, were sectioned and sampled. The samples were sequentially ground with water-based sandpaper of varying grit sizes, polished to a mirror finish, then etched with Keller reagent for 5–10 seconds, and ultrasonically cleaned. The microstructure of the samples under various test conditions was observed using an OLYMPUS GX71 metallographic microscope. The surface morphology of the samples after Keller reagent etching was examined using a NANO SEM430 field emission scanning electron microscope (FESEM) at a working voltage of 15 kV in secondary electron mode. Elemental distribution at the interface was analyzed using an energy dispersive spectrometer (EDS). The phase composition of the die castings was analyzed with an Ultima IV X-ray diffractometer, with a scanning range of 10°–90°. The hardness of the samples was measured using an HB ST-3000 digital Brinell hardness tester, with a test load of 5 N and a dwell time of 15 seconds. Tensile testing was conducted on a WDW-100G universal testing machine, with specimen dimensions following the GB/T 228.1-2021 "Metallic Materials – Tensile Test – Part 1: Room Temperature Test Method" standard and a tensile rate of 1 mm/min.