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- Crack Initiation (2)
- Critical Strain Rate (2)
- Hot Cracking (2)
- Solidification Cracking (2)
- 4043 Filler Alloy (1)
- 6060 Aluminium Alloy (1)
- Al-Mg-Si Alloy System (1)
- Aluminium Alloys (1)
- Aluminium alloy (1)
- Cast Microstructure (1)
- Cooling Rate (1)
- Crack Growth (1)
- Crack Prediction (1)
- Crack growth (1)
- Critical Strain (1)
- Minor Elements (1)
- Parameter Effects (1)
- Phase Constituents (1)
- Silicon Content (1)
- Solidification Path (1)
- Solidification cracking (1)
- Strain rate model (1)
- Weld Defect (1)
- Weld Metal Microstructure (1)
- Weldability Testing (1)
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 (TiAl3 + 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.
A perspective will be given that outlines important considerations in evaluating and predicting weldability. An examination will be made of the local conditions necessary for solidifications crack initiation and growth in a weld. This will be done in light of two prominent thermo-mechanical approaches involving critical strain and critical strain rate. Critical conditions will be identified based upon values available in the literature. Methods used to measure strain and strain rate will be compared. The interpretation of crack lenght measurements commonly used to quantify weldability will be questioned, based upon our current understanding of the problem. Complications and problem areas needing better definition will be identified and discussed, including strain distribution in the mushy zone, segregation at grain boundaries, effect of impurities, and effect of cooling rate on solidification path. Finally, a suggestion will be made for a new approach to weld development using in-situ strain rate measurements and new composition-strain rate maps that define the boundary between crack an no-crack conditions.
The occurrence of solidification cracking during welding remains a little understood phenomenon, in spite of extensive studies and tests performed to evaluate and compare the relative weldability of many different alloys. From an approach often adopted in the welding community attributed to Prokhorov, solidification cracks are believed to form when a critical tensile strain is exceeded, specific to the alloy, assuming that the mushy-zone has limited ductility. Tensile stresses and strains normally form behind a moving weld pool as a result of solidification shrinkage and thermal contraction, as influenced by welding parameters and the degree of restraint.