Hot cracking and stress corrosion are common issues. Specifically, s are great alloys for marine applications thanks to their low density and steel-like strength. In other words, a great alloy for your application does not equal a highly weldable alloy.
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Nominally matching filler metals are often employed for non-heat-treatable alloys. However, for alloy-lean materials and heat-treatable alloys, non-matching fillers are used to prevent solidification cracking. The choice of filler metal composition for the various weldable alloys is specified in BS EN Pt for TIG and MIG welding; recommended filler metal compositions for the more commonly used alloys are given in the Table.
Aluminium and its alloys can be readily welded providing appropriate precautions are taken. The most likely imperfections in fusion welds are:. Porosity is often regarded as an inherent feature of MIG welds; typical appearance of finely distributed porosity in a TIG weld is shown in the photograph. The main cause of porosity is absorption of hydrogen in the weld pool which forms discrete pores in the solidifying weld metal.
The most common sources of hydrogen are hydrocarbons and moisture from contaminants on the parent material and filler wire surfaces, and water vapour from the shielding gas atmosphere.
Even trace levels of hydrogen may exceed the threshold concentration required to nucleate bubbles in the weld pool, aluminium being one of the metals most susceptible to porosity. To minimise the risk, rigorous cleaning of material surface and filler wire should be carried out.
Three cleaning techniques are suitable; mechanical cleaning, solvent degreasing and chemical etch cleaning. In gas shielded welding, air entrainment should be avoided by making sure there is an efficient gas shield and the arc is protected from draughts. Precautions should also be taken to avoid water vapour pickup from gas lines and welding equipment; it is recommended that the welding system is purged for about an hour before use.
Wire brushing stainless steel bristles , scraping or filing can be used to remove surface oxide and contaminants.
Degreasing should be carried out before mechanical cleaning. Dipping, spraying or wiping with organic solvents can be used to remove grease, oil, dirt and loose particles. Solidification cracks form in the centre of the weld, usually extending along the centreline during solidification. View the Digital Edition. This magazine has served the welding community in North America well for more than 20 years.
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