Heat treatment of castings
Heat treatment of castings is the controlled heating, soaking and cooling of finished castings to change their structure and properties. In aluminum castings, it is used primarily to increase strength and hardness, relieve stresses and stabilize dimensions.
Not every casting requires it – many parts are used in the as-cast condition (F). Whether heat treatment is applied, and which type, depends on the alloy, the casting process and the requirements given on the drawing.
Types of heat treatment for aluminum castings
| Treatment | Purpose | Temper per EN 1706 |
|---|---|---|
| solution heat treatment i aging | highest strength and hardness | T4, T6, T64, T7 |
| artificial aging only, directly after casting | increased hardness and stabilization without the risk of blistering | T5 |
| stress relief annealing | removal of casting stresses and dimensional stability, e.g. before machining | – |
Solution heat treatment and aging together are precipitation hardening, commonly called hardening of aluminum. Solution treatment involves soaking the casting at approx. 480–545°C (depending on the alloy) and quenching it rapidly; aging involves holding it at ambient temperature or in a furnace, usually at approx. 150–180°C.
How to select heat treatment for a casting
- Alloy – alloys with magnesium and silicon (e.g. EN AC-42000) and with copper respond well to solution treatment and aging. EN AC-51300 (AlMg5) is used in the as-cast condition.
- Casting technology – permanent mold and sand castings can be solution treated. Die castings are usually only aged (T5), because gas trapped inside them forms blisters at high temperature.
- Drawing requirements – minimum strength, hardness and elongation for a given alloy and temper are specified in PN-EN 1706. It is advisable to state the alloy grade together with the temper in the documentation, e.g. EN AC-42000 T6.
- Shape and further processing – thin, long castings may distort during cooling, which is why final machining is usually performed after heat treatment.
Heat treatment and casting dimensions and quality
Rapid cooling after solution treatment introduces stresses and can distort the casting, while excessive temperature causes incipient melting at the grain boundaries. For this reason, the temperature, soaking time and quenchant are determined for the specific alloy and shape, and castings are arranged in the furnace so that they heat up and cool evenly. The result is verified by hardness measurement or tensile testing.
Heat treatment does not remove casting defects – porosity or misruns must be eliminated at the casting process stage. It has little effect on corrosion resistance; here the alloy composition and coating matter more.
In short: the most common heat treatment for aluminum castings is solution treatment and aging (T6 temper). Die castings are usually only aged (T5), and stress relief annealing removes stresses and stabilizes dimensions before machining.
Heat treatment of castings at our foundry
We perform heat treatment – annealing, solution treatment and aging – on customer request, as part of a complete production process: from pattern and casting, through CNC machining, to powder coating. We also perform strength testing on request.
Guides: aluminum hardening, aluminum solution treatment, aluminum aging, aluminum hardening and aluminum casting alloys.
Need aluminum castings with heat treatment? Send a drawing or 3D model to odlewnia@adjatech.pl or call: +48 61 662 43 37 (Mon–Fri 8:30 a.m.–4:30 p.m.).
Scope of services: foundry production capabilities.