From these studies, it is clear that the inappropriate selection of filler metal corresponding to base metals in the brazing process and improper welding tool position in the friction stir welding resulted in improper dilution between the base metals and filler metal.
Fatigue failure is caused by high value of maximum tensile strength, high amount of variation in applied stress, attachment of corrosion welds, improper flexibility, improper heat treatment, contouring of welds, large number of cycles of applied stress and cold-bend restriction to thermal expansion [55].
It is concluded that the damage cause was the impermissible quality of worldwide manufacture and improper production repair welding during manufacture.
In welded structures of aluminium alloys, hot cracking occurs as a result of inappropriate filler material, excessive base alloy dilution of weld metal and improper joint design (Guo et al. 2009).
Defects can occur in welded, brazed, or soldered joints because of improper joint design, improper joint preparation, improper process selection or operation, inherent material susceptibility to cold or hot cracking, or other defects.
Improper dilution (i.e. solubility) between the metals welded influences the microstructural formations and thus affects the mechanical properties of the weld metal (Joseph 2006).
The region where billet on billet welds develop is usually defective and represents a discontinuity in the extruded product, where improper quenching conditions associated to the stop of the line induce poorer mechanical properties.
Based on his allegations, the NEB found coating damage to a pipeline that appeared to go unreported for a year; an exposed, buckled section of pipe that was unnoticed for a year; an isolated mistake in welding procedures; a worker on site without protective equipment; an isolated incident of improper installation of ladders; and the over-torquing of a bolt that resulted in injury.
During friction stage of welding process, the particulates (SiC & Graphite) used for reinforcement, tend to increase the viscosity and lead to improper mixing of matrix and reinforcement.
