Heat treatment of forged metal products is when a finished part is subjected to medium-high temperatures (far less than forging temperatures) to normalize and modify the part’s internal structure. In doing so, it achieves slightly different chemical and material properties than the original forged part.
At Anchor Harvey, our proprietary in-house heat treatment process is coordinated with the rest of the production process to ensure a proper heat treatment on all production pieces. Not all parts need the same type of heat treatment, and heat treatment can mean a variety of slightly different processes that can achieve vastly different results. Our proprietary on-the-go heat treatment delivers results that exceed ASTM standards with a 15% improvement in component properties and is consistently recognized by major OEMs as "the best of all worlds" for providing superior components.
What is Heat Treating?
Heat treatment places a finished part into an oven and exposes it to low or medium heat to achieve a greater internal structure. On a microscopic scale, metals form into an organized crystalline structure whereby the metal atoms naturally form into a perfectly spaced atomic structure. However, metals don’t usually form so perfectly, instead, they form into uneven groupings. When multiple groupings align with each other in the same general direction, that is called a “grain.”
When metal is cold, the grains in metal are set and cannot move naturally. Grains can only be moved or manipulated through the application of heat, force, or both. During the forging process, the grain structure is massively realigned to achieve greater strength and ideal internal forces, but the forged part may have some misaligned grains that compromise the structure of the part. To solve this, the part is heated again to allow the grains to realign themselves into a more desirable formation.
Types of Heat Treatment
Heat treatment can be broken down into a few key processes:
- Annealing: The process of annealing refers to heating and cooling slowly to relieve internal stresses. This increases the ductility of the metal and reduces its hardness and brittleness. Parts often become tougher and stronger against bending forces but will deform much more easily than a hardened part. An annealed part's grain structure will include larger grains that are more aligned and can bend and shift without damage. Annealing is usually used to make a part easier to machine or work but is not often appropriate for finished parts.
- Precipitation Hardening: Also called artificial aging, a precipitation-hardened part is heated and cooled to create larger particles, or precipitates, of metal in an impurity phase that stops the movement of grains along dislocations. This distributes any alloying elements throughout a part to increase the quality of an alloy and greatly increases the hardness and tensile strength of a heated part.
- Solution Heat Treatment: Sometimes referred to as “quenching”, solution heat treatment refers to heating a part to disrupt its internal structure and then rapid cooling through exposure to various solutions (oftentimes water and/or oils). This rapid cooling “locks” the disrupted grain structure into place quickly, leading to a part that will continue to harden as it fully cools to room temperature.
Aluminum Heat Treatment
Anchor Harvey produces a few key standard temper designations for most forged aluminum parts:
- O (Annealed): This designation simply refers to a fully annealed part. This part is nearly as soft as possible for its base alloy, perfect for machining or more forge work.
- T4 (Solution Treatment and Naturally Aged): T4 tempered alloyed aluminum parts are initially solution treated to lock in a grain structure and then left to sit at room temperature for a few days. This allows the metal to harden, but without disrupting the quick artificial aging process.
- T6 (Solution Heat Treatment and Artificially Aged): T6 tempered alloyed aluminum parts are solution heat treated to initially harden the part and achieve a good grain structure and even solution of alloying elements. However, the final part is then precipitation hardened to gather some impurity phases and achieve a harder product than can be achieved through natural aging.
Anchor Harvey’s proprietary, on-the-go in-house heat treatment process is coordinated with the entire production process for a higher quality of forged aluminum parts. No matter what customers require, the complete forging shop at Anchor Harvey can ensure that your parts are engineered with every step in mind, forged with precision, and heat-treated to perfection all without ever leaving the premises. Request a quote today.