AWS PRGWA-QA pdf free download

AWS PRGWA-QA pdf free download.The Practical Reference Guide for Weldling Aluminum.
Laser Cutting
Laser cutting of aluminum tends to produce a rough cut with a surface finish exceeding 125 Ra, which are potential dirt traps. When laser cutting is utilized it should be performed on clean material so as not to spread surface contaminants into the molten cut zone.
Plasma Arc Cuffing
Plasma arc cutting is normally used for rough cuts of large plates. The “recast” cut surface is then machined for final preparation. Intergranular cracking can occur as deep as 0.090 in. from the cut edge of 2XXX, 6XXX, and 7XXX aluminum alloys, so machining must remove this zone.
Work Gloves
Work gloves, while important, are a common source of contamination. Obviously dirty gloves arc a contaminant. However “clean gloves” can be misleading as lint and other particles may be transferred to the weld zone surface. Lint and other foreign material entrapped in the weld can produce porosity. Lint has been known to produce fine “chain porosity.” For handling preweld clean surfaces, including weld details and tooling within the weld zone, use lint-free gloves, low-lint gloves, plastic throwaway gloves, or “kitchen-type” latex gloves. These gloves can also be used when manually feeding filler wire. The kitchen-type latex gloves are relatively thin with textured fingertip surfaces aiding in feeling and feeding the filler wire. They can also be washed and dried with warm air blow dryers while on the hand. The insides of the gloves are coated minimizing sweating and easing insertion of the hand. A clean, smooth leather glove is recommended for the hand that is holding the welding torch. When high amperages arc employed a clean, smooth leather glove can also be used to feed the filler wire. True lint-free gloves can be expensive and difficult to work in. Low-lint gloves are normally adequate and absorb body moisture and oils better. However, never turn the gloves inside out when removed in order to reuse them. This glove surface may appear clean, but will have been contaminated from contact with the skin.
Preweld Cleaning
It should be understood that contaminants will produce porosity. Common contaminants normally encountered are oxides, water stains, dirt, oil, grease, paint, fingerprints, pencil or ink marks, lint, and other foreign materials. Anodizing and other surface protections can produce contaminants too. Sometimes you can weld over these contaminants and get away with it but most times you cannot. It is not always consistent. However, clean conditions with good welding parameters will produce clean welds on weldable alloys. The entrapment of contaminants in the molten weld puddle causes the contaminants to out-gas or become inclusions. The out-gassing is then entrapped within the solidifying weld metal creating gas pockets (porosity). Porosity is a void, which reduces the cross-sectional area of the weidment.
The purpose of preweld cleaning is to prevent porosity and lack of fusion. One cause of lack of fusion on aluminum is contamination preventing the molten weld from alloying with the parent metal or the previously solidified weld metal. The contamination can act as a boundary membrane preventing alloying. Lack of fusion is similar to a man-made crack which is subject to propagation (growing) under thermal or mechanical stress conditions.AWS PRGWA-QA pdf download.