Certain questions always seem to return to torture novice engineers. No sooner has one problem been solved than the next comes careening down the track like a runaway train. It’s the different heat treatment terms that really create the deepest furrowed brows. Once and for all, we’re going to get rid of this tangle by injecting a heavy dose of clarity into metal transformation procedurals.

Abbreviating the Metal Hardening Process 

Furnace-hot temperatures send the metal workpiece towards its transformative thermal threshold. The microstructural components in that material change. They assume a special atomic relationship, which engineering types refer to as austenite. In this metal phase, the component is workable and corrosion resistant, but it’s hardly usable just yet because the metal is still red-hot. That’s why this is an ‘abbreviated’ description.’ Quenching, the next stage in the heat treatment process, rapidly cools the part, completes the treatment, and locks in the properties that were gained at the upper transformative temperature threshold. Metal hardening technology, therefore, injects the part with heat, whereas the metal quenching stage immediately removes that thermal load. In contemporary engineering methodologies, its water or oil that plays the part of the quenching agent.

Acquiring Metal Tempering Improvements 

There are misconceptions regarding the differences between metal tempering and metal quenching. That’s perhaps because of all the blacksmith scenes in old Hollywood movies. Viewers were told that the part was tempered when it was dropped in a wooden bucket of water, so they assumed the blade was now tougher and durable. In fact, the workpiece had been hardened. It was loaded with a martensitic grain, a form of steel that was brittle. The actual tempering operation was still waiting. Think of this as the process balancer, the heat treatment stage that removes brittleness but keeps the component hard enough to serve its purpose. This time the metal is heated to a lower temperature then allowed to cool until the ductility and workability ratio overwhelms the brittleness of the metal.

The tempered component is durable and corrosion resistant. Heat has been applied again, but it’s not the same near-melting hot thermal load that almost transformed the metal into a molten heap of smoking iron. Metal hardening is, therefore, an intensely hot, furnace-driven process. Metal tempering does again apply heat, but the thermal load is designed to transform the martensitic alloy, to cancel out the brittleness added during the hardening work. As for the metal quenching station, this is where the rapid cooling takes place, the immersion process that immediately removes the heat and locks in the desired mechanical properties.

When a discussion turns to heat treatment, aluminium isn’t the first metal that comes to mind. We think of its lightweight features, the uses of aluminium alloys as an aeronautics material and a commercial commodity. Be that as it may, there are thermally conditional aluminium alloys out there, forms of the abundant metal that can be heat treated. Starting with homogenizing, it’s time to investigate the heat treatment of aluminium alloys.

Aluminium Alloys: Heat Treatment Suitability

In its purest form, this is a soft metal. Composite variants alloy the pure metal so that it gains the capacity to achieve a transformative state when heat is applied. Interestingly, when alloyed with manganese or magnesium, the newly amalgamated alloy does not respond well to heat treatment. We need to turn to other metallic elements if we’re to accomplish this thermally transformative operation. These are the copper, magnesium silicide, and zinc alloying materials that enhance aluminium and gift the normally soft metal with greater strength.

Thermally Redistributing the Grain 

Aluminium alloys undergo a physical change when they’re processed, but that material alteration tends to precipitate outwards. Imagine an aluminium casting, a product that’s cooling. Due to the innate characteristics of the material, grainy crystals form against the cool casting surface. Basically, the metal substructure is unevenly distributed. It’s soft on the outside and harder in the centre of the casting. The product is not ready for application. The heat homogenizing process cooks the aluminium just below its melting point. The thermal energy then redistributes the alloying elements until all of the soft precipitates are eliminated.

Annealing and Solution Heat Treatment

If the lightweight metal alloy becomes work hardened, it’s no longer workable. Annealing heats the workpiece beyond its upper critical temperature (300°C to 400°C), then it holds that temperature for a predetermined period. The resulting microcrystalline ‘reset’ reintroduces slip planes, an important malleability feature that’s lost if the workpiece is work hardened. As for solution heat treatment, there are similarities between this method and annealing. The major difference, a quenching phase, stops age hardening while promoting a homogenized material structure.

Time is also a strong ally here, which means the hardening process can continue after the solution heat treatment work. Stored in sheds for several days, the age hardening occurs at room temperature as the grains “lock” in place. In conclusion, though, there are heat-treatable aluminium alloys. They’re divided into several numerically labelled groups. Copper alloyed aluminium forms the core of the 2xxx series, zinc hosts the 7xxx series, and magnesium/silicon amalgams occupy the 6xxx series. Before considering one of the above heat treatment methods, the correct aluminium alloy series must be sourced.