ISO 11881 pdf download.Corrosion of metals and alloys – Exfoliation corrosion testing of aluminium alloys
1 Scope
WARNING: This International Sandard may involve hazardous materials, operations and equipment. It does not purport to address all of the safety problems associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 1.1 This International Standard describes procedures for constant immersion accelerated exfoliation corrosion testing of aluminium alloys primarily for the purpose of research, development and quality control. 1.2 It covers aspects of the corrosive solution, specimen preparation, exposure, inspection and interpretation of test results. 1.3 This International Standard is applicable primarily to the testing of wrought aluminium alloys in the form of semi-finished mill products and parts produced both from conventional ingot metallurgy processes and from powder metallurgy processes, as well as aluminium alloy metal matrix composites including those produced by mechanical alloying. 1.4 It can also be used for testing ingots and cast aluminium alloys when oriented structures such as columnar grains or striated segregations are present. 1.5 The results of these tests are most applicable to research studies of trends in alloy development and should not be considered as an absolute criterion of the resistance to exfoliation. When these tests are used for production control of exfoliation-resistant materials, limits of acceptable performance should be the subject of an agreement between concerned patties.
2 Normative references
The following standards contain provisions which, through reference in the text, constitute provisions of this International Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and IS0 maintain registers of currently valid International Standards. IS0 3696:1987, Water for analytical laboratory use – Specification and test methods. IS0 8044:-’), Corrosion of metals and alloys – Basic terms and definitions. IS0 1 1846:1995, Corrosion of metals and alloys – Determination of resistance to intergranular corrosion of solution heat-treatable aluminium alloys.
3 Definitions
For the purposes of this International Standard the following definition as well as those given in IS0 8044 applies. 3.1 exfoliation corrosion stratified form of subsurface corrosion of susceptible wrought alloy mill products having a highly directional grain structure, accompanied by detachment of separate layers from the body of the material, formation of cracks and finally possible complete layer-by-layer disintegration of the metal (see also the definition of “layer corrosion” in IS0 8044) NOTE transgranular paths or a mixed intergranular/transgranular path.
6 Test specimens
6.1 Size There is no required size or shape but it is advisable that the specimen be not too small as visual inspection is the key evaluation method. It is recommended that flat specimens at least 50 mm x 75 mm in size and full section thickness with the specimen length oriented in the direction of principal deformation of the product be used when practicable. For convenience in handling during exposure, specimens of convenient thickness may be sawn from the surface region of thick sections or bulky products. For comparable results with a series of material variants, the size and shape should be one and the same. 6.2 Location The test surface for semi-finished products should be either the as-fabricated surface or some specified interior planes. Interior planes typically used are:These interior planes are representative of many of the exposed surfaces of parts machined for aircraft components and may expose regions in the grain structure with the highest exfoliation susceptibility. When removing test specimens from extrusions and forgings, specimen locations underneath flanges, ribs, etc.or where the grain structure is usually variable, shall be avoided. The test surfaces should be machined and/or chemically milled to produce a uniform surface free of heat treating films, alclad coatings, uneven surface layers of recrystallized grains, traffic nicks and scratches, etc. unless it is desired to test the metal in an as-received condition. 6.3 Machining When machining specimens for exposure of interior planes (T/lO, T/4, etc.) the final machining cut shall be a light one of about 0,635 mm or less to avoid the creation of a highly worked surface (an artifact which could influence the perception of exfoliation of relatively resistant materials). The roughness parameter of machined test surfaces, Ra shall not exceed 2,5 pm unless it is required to simulate an as-manufactured surface condition. The test specimens shall have edges dressed by machining or filing to a depth sufficient to remove deformed metal and residual short transverse tensile stresses. If the thickness of the sheared specimen is -= 3 mm the edges should be machined to a depth of 100 % of the specimen thickness, and if its thickness is 3 3 mm, the edges should be machined to a depth of at least 50 % of the thickness.