This International Standard specifies quality levels for imperfections in arc-welded joints in aluminium and its alloys. It applies to material thicknesses above 0,5 mm. It covers full-penetration butt welds and all fillet welds. The principles of this International Standard may also be applied to partial-penetration butt welds. Quality levels for beam-welded joints are presented in ISO 13919-2. Three quality levels are given in order to permit application to a wide range of welded constructions. They are designated by symbols B, C and D. Quality level B corresponds to the highest requirement on the finished weld. The quality levels refer to production quality and not to the fitness for purpose (see 3.2) of the product manufactured. This International Standard applies to: — all types of weld, e.g. butt welds, fillet welds and branch connections; — the following welding processes and their sub-processes as defined in ISO 4063: — 131 metal inert gas welding (MIG welding); gas metal arc welding /USA/, — 141 tungsten inert gas welding (TIG welding); gas tungsten arc welding /USA/, — 15 plasma arc welding; — manual, mechanized and automatic welding; — all welding positions. Metallurgical aspects, e.g. grain size, hardness, are not covered by this International Standard.