American Machinist

Weldability of aluminum-lithium alloys.

Weldability of aluminum-lithium alloys

MAINLY BECAUSE OF THEIR high rigidity and lighter weight than conventional aluminum alloys, aluminum-lithium alloys hold promise for structural applications in aircraft, aerospace vehicles, and rocket-motor cases, some of which are apt to call for welding, primarily GMAW and GTAW. But just how weldable are these alloys?

The lithium is beneficial, reported Martin Marietta researchers headed by Staff Engineer Carl E. Cross of the Astronautics Group (Denver) at ASM Intl's (Materials Park, Ohio) Weldability of Materials Conference in Detroit last October. "Comparable to the best conventional aluminum alloys" as to susceptibility to hot tearing--the usual criteria--noted researchers affiliated with Comalco Ltd (Australia), referring to the company's new XT aluminum-lithium alloys at the conference.

Composition is key influence

The Martin Marietta researchers, who focused on Alcoa's 2090, Pechiney's 2091, Alcan's 8090, and Martin Marietta Laboratories' Weldalite 049 (produced under license by Reynolds Metals), noted that alloy composition is the dominant influence on susceptibility to hot tearing: weldmetal fracture due to shrinkage during solidification. Other factors, such as joint geometry and restraint, heat input, and thermal gradient also affect this susceptibility but, if these variables are held nearly constant, substantial variations in hot tearing still usually occur, indicating the overriding influence of composition.

In most tests used to assess susceptibility to hot tearing, welding strain is augmented to promote tearing, and the degree of tearing is then quantified by measuring total accumulative crack length (TCL), the researchers noted. …

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