Aluminum weld defects

Metal Preparation. Sheet-steel parts are formed by stamping, bending, and shearing. Many parts require welding (qv), which needs to be carried out in a uniform, smooth manner so that the welded joint can be enameled without defects. Cast-iron parts are formed by the usual cast-iron foundry methods however, additional care is given to prevent contamination of the surface. Surface contamination causes defects in the enamel, particularly bUsters and bubbles. Aluminum metal can be formed in sheets, extmsions, and as castings. 

Several researches have examined the effect of tool dimensions on friction stir weld quality. Reynolds and Tang (Ref 11) used several different variations of cylindrical pins with a concave shoulder to show that defect-free friction stir welds in 8.1 mm (0.32 in.) thick 2195 aluminum alloys could be produced with pin diameter to shoulder diameter ratios ranging from 2 to 1 to 3.125 to 1. Peel et al. (Ref 115) evaluated cylindrical pins with either a standard metric M5 thread (5 mm wide with 0.8 mm pitch) or a wider pin (6 mm wide) with a coarser thread (1 mm pitch). At higher travel speeds (200 mm/min, or 8 in./min), the broader 6 mm tool with the coarser threads was more effective in disrupting the faying interface between the two joined workpieces. This change of pin design... 

In composite materials, flaws, bonding faults and internal defects have all been examined using liquid crystal thermography, [177-184]. Surface and subsurface flaws have been detected, including regions of unstable plastic flow in aluminum alloys (Lueder lines) [185], faults in welded metals [186], and cracks, voids and leaks in pressure vessels [187-188]. Potential fracture sites have been determined in metals... 

---