Weld Parameter and Minor Element Effects on Solidification Crack Initiation in Aluminium

Abstract

Earlier work has established that a critical amount of 4043 filler is required to avoid solidification cracking when arc-welding 6060 aluminium, depending upon local strain conditions. For example, when the mushy zone behind the weld pool experiences a tensile strain from combined thermal and shrinkage stresses, the possibility exists for crack initiation. For a greater rate of strain, it has been determined that a greater 4043 dilution (i.e. higher weld metal silicon content) is required to avoid crack initiation. Making use of the Controlled Tensile Weldability (CTW) test and local strain extensometer measurements, a boundary has been established between crack and no-crack conditions for different local strain rates and filler dilutions, holding all other welding parameters constant. Using this established boundary as a line of reference, additional parameters have now been examined and their influence on cracking has been characterized. These parameter influences have included studies of weld travel speed, weld pool contaminants (Fe, O, and H), and grain refiner additions (TiAl 3 + Boron). Each parameter has been independently varied and its effect on cracking susceptibility quantified in terms of a critical strain rate required to initiate cracking for a given 4043 filler dilution.

Effect of weld travel speed on solidification cracking behavior. Part 2: testing conditions and metrics

“…Using the Controlled Restraint Weldability (CRW) test showed that increasing welding speed and simultaneously laser power reduces the solidification cracking susceptibility [41]. This is in agreement with arc weldability data [7,32] but in opposition with some laser weldability data [10,30]. This disagreement may possibly arise from the methodology as other works maintain constant laser power while varying welding speeds.…”

“…Nevertheless, these results cannot be used to investigate only the welding speed effect as the filler dilution varied with welding speed. Indeed, maintaining constant wire feeding rate while increasing welding speed leads to smaller filler dilution and higher susceptibility to cracking [31,32] and it has been indeed shown that weld metal silicon content varied for the different welding conditions [30]. Such metallurgy-speed interaction is also true for MIG and MAG welding processes, and therefore care must be taken in generalizing conclusions.…”

“…Measuring crack length metrics or crack-no crack macro-conditions [15,43,59,62,63] will provide an overall point of view of the interaction between microstructure and process-induced thermo-mechanical fields. However, if local measurements are applied [31,55,56,64], then thermal-induced strains are not accounted for and only the inherent susceptibility of a microstructure to cracking are evaluated. Therefore, increasing welding speed may lead to a more susceptible microstructure (e.g.…”

Surface- and volume-based investigation on influences of different Varestraint testing parameters and chemical compositions on solidification cracking in LTT filler metals

“…μCT analysis is able to back up this finding. This behaviour was attributed to conflicting influences of weld pool geometry and solidification characteristics for varying energy inputs or welding speeds [60], yet additional investigations are required to fully explain these results. Cracking in alloy H was found to be triggered by higher stroke rates.…”

Effect of weld travel speed on solidification cracking behavior. Part 1: weld metal characteristics

“…Large stray grains were observed above 4 mm•s -1 ( Figure 6 ) causing a deterioration in solidification cracking resistance. Using the Controlled Tensile Weldability (CTW) test, the critical strain rate for solidification crack formation dropped from -0.06 to -0.20 %•s -1 when increasing welding speeds from 2 to 6 mm•s -1 [19]. Faster welding velocities were investigated for autogenous GTA full-penetration welds on 3 mm-thick sheets of 1050A, 6082, and 5083 aluminum alloys [16].…”