Processing and Properties of Allvac® 38-644 Alloy for Titanium Automotive Suspension Springs

The metastable beta titanium Allvac® 38-644 Alloy (Ti-38-644) has a long history of use for aerospace springs and fasteners. A vast range of mechanical properties is attainable for this alloy by manipulating the processing plan and adjusting subsequent thermal treatment. Ti-38-644 aerospace parts are typically processed in accordance with AMS 4958 for solution treated parts and AMS 4957 for cold drawn parts. Neither of these specifications is particularly amenable to the high volume, low cost needs of the automotive suppliers. An ongoing project at Allvac has recently focused on adjusting the processing procedure and thermal treatment of Ti-38-644 to improve its viability and cost for the automotive suspension spring market. After the hot rolling process, particular attention has been given to cold drawing procedures and subsequent thermal treatments of 30 minutes or more. The combination of a low level of cold work and short aging time has been found to result in a better balance of properties than ascertained by the AMS specifications. In addition, the short aging times are less disruptive to the manufacturing cycle and offer the potential for elimination of the post-process pickling procedure which is common for aerospace titanium parts. It is anticipated that the improved processing and associated cost reduction of Ti-38-644 will be an instrumental tool for near-future automotive vehicle weight reduction.