tailieunhanh - The Welding of Aluminum & Its Alloys Part 3

Tham khảo tài liệu 'the welding of aluminum & its alloys part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 3 Material standards designations and alloys Designation criteria Aluminium alloys may be divided into two broad classes cast and wrought products. These two classes can be further subdivided into families of alloys based on chemical composition and finally on temper designation. Temper designations are used to identify the condition of the alloy in other words the amount of cold work the alloy has undergone or its heat treatment condition. There are a number of schemes available for identification of the alloy and its condition. In this book the numeric method adopted by the European Committee for Standardisation CEN will be used as standard. This system uses four digits to identify the wrought alloys and five digits to identify the cast alloys and is broadly the same as the ISO and US numerical methods of identification where a four digit number identifies the unique alloy composition. This is in agreement with the recommendation made in the early 1970s for an International Designation System issued by the Aluminum Association in the USA. The chemical composition limits specified in the CEN specifications are identical with those registered with the Aluminum Association for the equivalent alloys. This should simplify the sourcing of alloys and remove the confusion that can surround the identification of specific grades. One perennial problem for the welding engineer is the use of superseded specification designations to identify alloy compositions. As an aid to identification a table of comparative specification designations is included as Appendices C and D. Alloying elements The principal alloying elements are copper silicon manganese magnesium lithium and zinc. Elements such as nickel chromium titanium zirconium and scandium may be added in small amounts to achieve specific properties. Other elements may also be present in small amounts as unwanted impurities. These elements known as tramp or residual elements have no 35 36 The welding of aluminium and