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In-situ radiographic aluminum welding experiments were set up to observe the porosity formation and movement in aluminum weld pools. Aluminum Alloys 1100, 4047, and 6061 were autogenously gas tungsten arc welded while digitally recording radiograph images of macropores. Hydrogen was added in controlled parts per million through an argon-hydrogen shielding gas. The shielding gas hydrogen varied between 0 and 1000 parts per million of hydrogen, and three travel speeds were tested: 1.69, 2.54, and 3.39 mm/s. The transfer of hydrogen from the arc plasma to the weld pool was characterized using postweld gravimetric measurements to get the total pore volume and calculate weld metal hydrogen content. The amount of hydrogen added through the shielding gas played an important role in macropore volume and growth rate. Welding travel speed likewise played a critical role in hydrogen pickup. Alloy 1100 macropores originated at the bottom of the weld pool and then migrated upward toward the rear of the pool. Macropores in Alloys 4047 and 6061 originated at the leading edge of the weld pool and then moved downward and toward the rear of the pool. It is hypothesized that this difference in behavior is related to Marangoni-controlled fluid flow in Alloys 4047 and 6061. [ABSTRACT FROM AUTHOR]

One defect encountered in the fusion zone when welding aluminum alloys involves solidification cracking (i.e., the tearing apart of grain boundary liquid films at the trailing edge of the weld pool). This problem can often be mitigated by the proper selection of filler metal. Two key engineering examples, one aerospace and one maritime, where this has occurred were examined in terms of alloy development to achieve optimum mechanical properties while maintaining weldability. Specifically, base metal/filler metal systems susceptible to cracking were examined in terms of filler metal dilution. A mechanism for crack growth was presented based upon critical strain rate. Conditions needed for improved weldability through grain refinement were defined based upon the columnar-to-equiaxed solidification theory. [ABSTRACT FROM AUTHOR]