Effect of laser beam welding on tear toughness of a 1420 aluminum alloy thin sheet

A tear test has been conducted for a 1420 Al-Li alloy thin sheet and its laser welded joint. The test was based on the ASTM B 871-01, standard test method for tear testing of aluminum alloy products. Moreover, the hardness distribution and microstructure of the alloy and welded joints were investigated. The test results indicate that there exists slight orientation dependence of tear energies for the L-T and T-L base metal. In addition initiation energies are higher than the propagation energies for all the tear test specimens, and the tear energies of base metal are higher than those of weld metal and HAZ. Thus, it is considered that the tear toughness of the laser-welded joints is obviously decreased for the 1420 Al-Li alloy thin sheet. Fracture surface shows strong delamination structure for the base metal. Moreover, there exists a feature of fracture along grains or subgrains for the weld metal. Thus, the obvious decrease in tear toughness of weld metal is due to the transition of fracture mode from transgranular to intergranular.