Weldability Study of Aluminum Alloys Using Weld Simulation and Complimentary Variable Restraint Testing

Abstract

Aluminum alloys containing lithium are attractive to the aerospace industry. The high specific strength and stiffness of these alloys improves lift efficiency, fuel economy and performance and increases payload capability. The objective of this study was to compare the fabricability of six different aluminum base alloys. Three were Li containing alloys, two variants of AL 2195 (Al-4Cu-1Li) and a lithium enhanced analog of AL 5083 (Al-4Mg-2Li). Three were materials in common usage, Al 2219, Al 2014 and Al 5083. Fabricability was assessed using Gleeble thermomechanical testing, Varestraint testing and differential scanning calorimetry (DSC). Results indicate that Alloy 2195 is more susceptible to hot cracking than both Al 2219 and Al 2014. Cracking sensitivity is a strong function of chemical composition within specification ranges for Al 2195. Results also indicate that the lithium containing analog of Al 5083 is more hot crack susceptible than its parent material. Fabricability was correlated to material microstructure using optical microscopy, scanning electron microscopy and microprobe analysis. Hot cracking in all materials was associated with persistent, continuous liquid films produced by weld thermal cycling, aggravated by base material structure. Measures of several characteristic temperatures using the Gleeble simulator were fully consistent with Varestraint results. The maximum crack length in the Varestraint test correlates well to the liquidus temperature for the alloy less the nil ductility temperature. The temperature difference is equivalent to the thermal gradient associated with welding times the maximum crack length.