Volume 5, Issue 10 (November 2008)
Using Polyalkylene Glycol Quenchants to Effectively Control Distortion and Residual Stresses in Heat Treated Aluminum Alloys
Polyalkylene glycol quenchants (also commonly called “glycol” quenchants throughout the industry) were introduced into the aluminum heat treating industry in the mid 1960s and immediately became the most important tool for reducing quenching distortion in sheet metal alloys. Later, the feasibility and benefit of glycol quenching thicker products, such as castings and forgings (which were normally quenched in hot or boiling water), was proven. Specifications were changed to permit glycol quenching of forgings and castings. However, because of a lack of understanding of the technology, the original benefits achieved in sheet metal distortion control and optimum distortion and residual stress control of thicker products has diminished. Currently, there is a significant lack of understanding regarding glycol quenching and, as a result, the full benefit of this technology is not currently being utilized. Distortion of sheet metal products and precision forgings has increased, resulting in increased check and straightening costs and higher residual stresses being imparted to parts. The realization of the benefits of glycols being able to reduce residual stress and ultimately machining costs is waning due to the reluctance of many engineers to recognize and understand the benefits of expanding the limits of the technology to achieve results not heretofore achievable. It is the purpose of this paper to review the basic concepts regarding glycol quenching of high strength aluminum alloys and to present recommendations for optimum control of distortion and residual stresses using the products. Specific illustrations showing that the proper use of glycol quenchants can provide the producer significant savings by (1) reducing quenching distortion and (2) minimizing residual stresses (which significantly improve machining practices and reduce the generation of scrap) are provided.