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.

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

Ultrasonic‐assisted tungsten inert gas welding was carried out on a thin plate of 2195 Al‐Li alloy, and the characteristics of the weld pores were analyzed in terms of their size and porosity. The effects of welding speed and ultrasonic power on the porosity and size of the pores were investigated. The pores were found to occur primarily adjacent to the surface of the weld. The porosity decreased and the size increased with a decrease in welding speed. The effect of ultrasonic power on the characteristics of the pores was different from that of the welding speed. The porosity and size of the pores decreased and then increased with an increase in ultrasonic power. A relationship was found between the transient cavitation intensity and the characteristics of pores. An increasing transient cavitation intensity results in a decrease in the porosity and size of pores when the transient cavitation intensity is lower. However, it can result in an increase in the porosity and pore size when the transient cavitation intensity further increases. Finally, the influencing mechanism of cavitation on welding pores was discussed.

Study on Pores in Ultrasonic‐Assisted TIG Weld of Aluminum Alloy

Microstructural characterization and mechanical performance of Al–Cu–Li alloy electron beam welded joint

Aluminium–lithium (Al-Li) alloys are very attractive for aerospace applications due to their outstanding properties, such as high specific strength, high rigidity and good resistance to corrosion and fatigue, compared to conventional aluminium alloys. The butt joints of Al-Li 2A97-T3 alloy sheet produced by fibre laser welding with ER2319 filler wire were investigated in this paper. Uniaxial tensile tests have been performed to determine the nominal mechanical properties of the joints with and without porosities. In addition, a defect zone was defined in the welded specimens to investigate the effects of porosity on the joint tensile behaviour. The post-weld strength prediction (PWSP) model in a previous study has been extended by including the effects of the porosity in the welds to predict the overall response of the butt joints. The experimental and the modelling results show a good agreement, with the yield strength having a deviation lower than 5%. Both the yield strength and the ductility of the tensile specimens were observed to have decreased with the presence of porosities. The porosities aggravated the inhomogeneous deformation in the weld zone. Higher strain rate was found in the defect area than the remaining weld zone during plastic deformation, as the porosity in the specimen caused inhomogeneous deformation. It was found that this accelerated the failure of the specimen and lowered the global ductility significantly.

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Effect of porosities on tensile properties of laser-welded Al-Li alloy: an experimental and modelling study

Effect of welding speed on microstructure and corrosion resistance of Al–Li alloy weld joint

The effect of TIG welding on the mechanical behavior of Al–Li alloy 2091-T851 has been investigated by means of tensile and fatigue testing. Compared to the base alloy, as-welded joints were found to display significant reductions in both tensile and fatigue strengths and to suffer a drastic degradation in ductility. Such behavior is primarily related to the presence of large elongated R phase precipitates at the weld metal grain boundaries, which leads to intergranular crack propagation through that part of the joint. Substantial microstructural changes, though, can be induced in the weld metal by subjecting the welded joints to a post-weld T6 type heat treatment. This promotes dissolution of the R phase, thus enhancing the tensile properties as well as the fatigue strength, consistent with the predominance of transgranular fracture of the weld metal in the heat treated joints. Finally, the microstructural aspects presented above indicate that the weld metal is plastically more heterogeneous than the base alloy and therefore is expected to work-harden faster, which is borne out by the tensile test results.

S.O de Menezes

Papers

Effect of weld metal microstructure on the monotonic and cyclic mechanical behavior of tig welded 2091 Al–Li alloy joints