What Are T4 and T6 Heat Treatments of Aluminium? Solution, Quench and Ageing

Many aluminium parts — from cast wheels to automotive suspension components — only reach their required strength through heat treatment. T4 and T6 are the two most common tempers. Both apply to precipitation-hardenable alloys such as casting alloy A356 (AlSi7Mg) or 6xxx wrought alloys.

1. Solution treatment

The part is held for several hours at a temperature slightly below the alloy's solidus (typically around 530–545 °C for A356) to dissolve alloying elements such as Mg and Si into the aluminium matrix. Temperature uniformity in the furnace is critical: too hot causes local melting, too cold leaves elements undissolved.

2. Quenching

The part is cooled rapidly, usually in water or a polymer solution, to trap the alloying elements in a supersaturated state. The key parameter is the quench delay — the time between leaving the furnace and entering the quench. The longer it is, the more the part cools in air and the lower the final strength. With thin sections, even a few seconds can matter.

This is the main advantage of tower (drop-bottom) heat treatment furnaces: the load basket is lowered vertically into a quench tank directly below the furnace, keeping the delay to a few seconds.

3. Ageing

• T4 – natural ageing: the quenched part is left at room temperature; strength increases by itself over days. Ductility is high, strength lower than T6.
• T6 – artificial ageing: the quenched part is held at a lower temperature (typically 150–180 °C for A356) for several hours. Fine precipitates form and yield and tensile strength rise significantly.

Exact temperatures and times depend on the alloy, section thickness and target properties; the values above are only indicative.

What matters in the furnace?

• Temperature uniformity: circulation fans and well-placed heaters for a narrow band across the whole load.
• Fast, safe quenching: short, repeatable quench delay, water temperature control and agitation.
• Recording and traceability: a temperature–time record for every load.
• Separate ageing furnace: at high volumes, doing solution and ageing in separate furnaces increases throughput.

OEM FURNACE tower-type T4/T6 heat treatment furnaces are designed around these needs and can be supplied as a complete line together with ageing furnaces.

Let us help you choose the right furnace. Send us your capacity, alloy and energy supply and we will prepare a clear, itemised quotation: talep@oemfurnace.com.tr · +90 533 945 27 94