Work hardened metals are difficult to form. The machining and shaping work has impacted the material in such a way as to cause the metal’s grain to compact and shrink. The processed alloy is now tougher but it’s also brittle, next to impossible to deform without incurring a material weakening fracture. Fortunately, we can reset a metal’s ductile properties by annealing it, thus phase transforming the alloy and returning lost workability to its internal structure.
Are All Metals Susceptible to Work-Hardening?
Every alloy suffers in some way from the stresses encountered in a machine workshop, but alloys of copper are particularly prone to these hardening effects. The grain of brass and bronze becomes smaller when it’s hammered and cut, which means the once malleable material no longer bends easily. Pure copper acts in the same manner, and so does a number of the most popular aluminium alloys. In fact, these non-ferrous metals are all renowned for their ductile properties, but those selfsame properties are lost or simply drastically attenuated unless we recruit an annealing stage.
The Annealing of Copper Alloys
We see examples of bronze parts cut into intricate shapes. Meanwhile, brass tubing angles around sharp corners, angles that mirror the dexterous twists and turns of a bronze product. Many engineering processes are used to create these curvilinear outlines, plus individual components require exact cutting in order to satisfy the scale of the project. A work hardened part is a likely result of this machining, which means no more bending or complex shaping can take place. The component requires annealing, a passage through a hot oven. The heat treatment process softens the metal, which restores ductility and much-needed malleability to the part.
Restoring Equilibrium to Aluminium and Stainless
Localized and complete heat treatment work anneals aluminium so that it can be formed into beautifully formed fences and geometrically detailed outlines. The lightweight metal is tough and more than a match for mild steel, but it requires this heat treatment stage to ensure its ductile characteristics are retained throughout the machining stage. Conversely, stainless steel favours a toughened material profile, but work hardening does reinforce an already formidable resistance factor. This heat treatment stage once again restores the robust alloy to its state of equilibrium.
An annealing station softens copper alloys. The result is a restoration of the metal’s predominant state, that of a supremely malleable alloy. Similarly, stainless metals are stress relieved and stabilized.