Alloy Heat Treatment have 20 furnaces (16 capable of solution treatment) including top loading, front loading and rapid quench (10 second) drop bottom furnaces, most national and international standard requirements can be met for aluminium heat treatment.
Ranging from sheet metal to large sand castings, a few grams to 2.5 tonnes, we have the capacity and the volume to heat treat a wide variety of aluminium products.
Largest solution furnace volume = 11.56m³ (2.15m x 2.15m x 2.5m)
Our range of water and polymer quenchants enable control over distortion and residual stresses in all components.
The Technical details:
Solution treatment is the process of solid state dissolving of key alloying elements (Solute Metals) within the aluminium (Solvent Metal) at the solution treatment temperature (typically between 450 and 550ºC depending on alloy grade). At the solution treatment temperature, sufficient time (soak time) is given to allow maximum solid solubility of the Solvent Metals in the Solvent Metal, to create a Super Saturated Solid Solution (SSSS). Without prior solution treatment, at room temperature, solid solubility of Solute Metals is relatively low, and is regarded as fully precipitated (not to be confused with precipitation hardened).
Solid solubility of key Solute Metals within the Solvent Metal increases as temperature increases. Maximum solid solubility is reached when the product is near melting temperature, hence, the importance of critical furnace controls to prevent insipient melting of the products being processed. However, once the SSSS is established, if cooling rate from the SSSS temperature to 100ºC or below, is too slow, Solute Metals will precipitate from the Metal Solution, resulting in products which will have poor response to ageing.
To entrap the SSSS at room temperature, precipitation must be prevented by rapid cooling of the alloy product from the solution temperature to less than 100ºC (quench delay time). The critical quench delay time depends on alloy grade and material thickness. Products in excess of 0.8mm should be quenched in less than 10 seconds, where quench delay time is taken from when the furnace door starts to open to when products are 100ºC or less. It is usual practice to quench solution treated parts into a tank of agitated water (10-100ºC depending on alloy) or agitated polymer solution (12-40%, 40ºC max typically, depending on alloy and/or thickness).
Temper designations for the freshly solution treated and quenched state is: W or AQ.
Once quenched, parts are very soft and ductile, but the onset of precipitation (aka ageing) hardening commences immediately. The onset of ageing can be significantly retarded by immediate post quench deep refrigeration of the products, typically -25ºC. In the deep frozen state, products remain soft and ductile enough to enable removal of any quench distortion (termed as Setting), with minimal risk of cracking. The typical time window for setting is 2 hours for wrought products and 4 hours for cast products.
It is recommended practice for set products to checked for cracks after full heat treatment, using Dye Penetrant Inspection (DPI) aka Dye Pen.