Uphill Quenching of Aluminum Alloys: A Process Review

Abstract. This paper describes the concept of Uphill process and its application  in the heat treatment of aluminum alloys such as large aerospace components. This technique  is often not well understood and there are relatively few publications about this. This process was originally developed  by Alcoa approximately 50 years ago for aluminum alloys.  It has also been referred to  "deep freezing" or "tri-cycle stress relieving". Uphill quenching is  interesting from the point of view of residual stress reduction which  may exceed 80%.Therefore, uphill quenching is typically used to  achieve dimensional stability in several types of aluminum parts. Often, it is applied after quenching and before aging. Assuming  that most of stresses that appear in heat treatment of aluminum alloys are due to the quenching process,  this intermediate technique becomes an effective tool when applied following  heat treatment. The uphill quenching  process  consists of the immersion of the part in cryogenic environment and after cooling is immediately followed by transfering to a hot-steam fixture to obtain a temperature gradient to maintain the mechanical properties gained with the heat treatment.  When properly performed, uphill quenching results in low residual stresses and better dimensional stability. The aim of this paper is to review the uphill quenching process compared with conventional quenching results.

 

Keywords: Uphill, Liquid Nitrogen, Quenchant, Aluminum alloy, Residual Stress Relief, Heat Treatment.