Aluminum castings in construction (Eurocode 9)
Eurocodes 9 includes recommendations for use in construction:
- deformable thermally hardenable aluminum alloys;
- thermally deformable aluminum alloys neuprochnyaemyh;
- castings, from cast aluminum alloys, as a thermally hardenable, and thermally hardened.
Below is presented overview Eurocode recommendations 9 on cast aluminum alloys. For professional application of Eurocode recommendations, use its authentic text with the appropriate national application.
Aluminum Castings in Eurocode 9
European standards, identified by cast aluminum alloys, are:
- EN 1676 - for aluminum ingots (ingots);
- EN 1706 - for aluminum castings.
The chemical composition of cast aluminum alloys in pigs and in finished castings is slightly different.
The designation of aluminum cast alloys in these standards consists of five numbers, before which an alphabetic "prefix" is written:
- "AW AB-" - for ingots, for example, AW AB-42100;
- "AW AC-" - for castings, for example, AW AС-42100.
Eurocodes 9 recommends six cast aluminum alloys for use in building structures (table 1, we omit prefixes for brevity):
- four thermally hardenable alloys 42100, 42200, 43000 and 43300, and
- two alloys, which are not hardened by heat treatment - 44200 and 51300.
Table 1 - Cast aluminum alloys for construction applications
All six cast aluminum alloys have a low copper content and therefore have good corrosion resistance..
Thermally Hardened Cast Alloys
Casting aluminum alloys 42100, 42200, 43000 and 43300 are alloys of the Al-Si-Mg system and, Consequently, thermally hardenable. All four alloys are suitable for sand and permanent casting., but usually not applicable for injection molding. The highest strength reaches alloy 42200 able to T6, but with lower ductility, than an alloy 42100.
Alloy 43300 shows the best casting properties and has mediocre corrosion properties, good machining and good weldability.
alloys 42100 and 42200 exhibit good enough casting properties, good corrosion resistance and good machinability.
Casting alloys, not hardened
Casting aluminum alloys 44200 and 51300 designed for sand and multiple casting, but not recommended for injection molding. Alloy 44200 has excellent casting properties, however alloy 51300 has rather mediocre casting properties and therefore is suitable only for more simple castings. Alloy 51300 has the highest strength, excellent corrosion resistance and good machining.
Alloy 51300 can be decorative anodized.
Minimum strength properties of aluminum castings
The minimum values of the conventional yield stress (0.2 %) and ultimate strength (ultimate tensile strength) for any place of the casting are given in the table 2. These values are 70 % from values, specified in EN 1706, which apply only to separately cast test pieces. Similarly, the limiting values of elongation A50 make up 50 % from specified in EN 1706 quantities.
Table 2 – Minimum mechanical properties of castings from aluminum alloys
Designing aluminum castings for construction
The design of supporting aluminum castings for use in construction is carried out on the basis of linear elastic calculation by comparing the calculated equivalent stresses with the calculated strength. Design strength should be less than tensile strength and conditional yield strength, which are multiplied by the corresponding reduction factors. These reduction factors are set in the national Eurocode annexes. 9.
The technical delivery conditions for each aluminum casting must include the following information:
- areas with tensile voltages, in which stresses are more than 70 % from the design strength (area H);
- areas with tensile voltages, in which the stresses are from 30 to 70 % from the design strength (area M);
- areas with compressive voltages, in which the stresses are from 100 to 30 % from the design strength (area M);
- areas of, in which stresses are up to 30 % from the design strength (area N);
- place and direction of cutting samples for mechanical testing. The cut point should be exactly in that place., in which there are maximum stresses for a given part or close to it. If the casting has several areas with high stresses, then the cutting of samples is carried out in more, than one place;
- all tests, which should be carried out;
- required minimum strength and elongation.
Quality requirements for building aluminum castings
To check the mechanical properties of the loaded areas of the casting, two finished castings from the batch are selected. In some cases, casting places with difficult casting conditions are also tested.. Tensile strength test results, conditional yield strength and elongation should be not less than values, indicated in the table 2.
Limitations on internal defects
1) Cracks in castings are not allowed.
2) Maximum permissible porosity:
- in areas H: 4 %;
- in areas M: 6 %;
- in areas N: 8 %.
The pore diameter should be less 2 mm.
3) Each casting must be subjected to:
- flaw detection by capillary methods to identify external cracks and
- X-ray flaw detection to detect internal defects.
Source: European standard EN 1999-1-1:2014