Application reference to gas shielded arc welding of Aluminium
The use of aluminium and its alloys increases continuously all over the world. In the fi eld of mobility an over proportional increase and further substitution of steel in particular, but not only, will occur in a near future. Increasing costs of energy make lightweight design more economical than ever. As a consequence, constructors switch from steel to aluminium and new manufacturers immediately start with aluminium.
As production processes and applied terminology offen differ only slightly from steel, basic mistakes are commonly made and lead to expensive rework, reject and delay. As a matter of fact, some properties of aluminium are just opposite to steel and knowledge about these is essential for safe manufacturing.
| Properties | Unit | Al | Fe | Relation |
| Atomic weight | [g/Mol] | 26,98 | 55,84 | ~ 1 against 2 |
| Crystal lattice | cubically face-centered | cubically body-centered | ||
| Density | [g/cm³] | 2,70 | 7,87 | ~ 1 against 3 |
| Modulus of elasticity | [Gpa] | 67 | 210 | ~ 1 against 3 |
| Coefficient of expansion | [1/K] | 24 * 10-6 | 12 * 10-6 | ~ 2 against 1 |
| Yield strength Rp0,2 | [MPa] | ~ 10 | ~ 100 | ~ 1 against 10 |
| Tensile strength Rm | [MPa/] | ~ 50 | ~ 200 | ~ 1 against 4 |
| Specific heat | [J/kg*K] | ~ 890 | ~ 460 | ~ 2 against 1 |
| Heat of fusion | [J/g] | ~ 390 | ~ 272 | ~ 1,5 against 1 |
| Melting temperature | [K] | 933 | 1811 | ~ 1 against 2 |
| Heat conductivity | [W/m*K] | 235 | 75 | ~ 3 against 1 |
| Electrical conductivity | [m/Ω*mm²] | 38 | ~ 10 | ~ 4 against 1 |
| Oxides | Al2O3 | FeO / Fe2O3/ Fe3O4 | ||
| Melting temperature of Oxidesder Oxide | [°C] | 2050 | 1400 / 1455 / 1600 | With Fe similar to metal; with Al three times as much |
| Density of Oxides | [g/cm³] | 3,89 | 5,7 / 2,4 / ~ 5,0 | Fe-Oxides are ligther than metal, Al-oxide is heavier |
Effects of the differences between the physical properties of steel to aluminium on fusion welding
The differences in density, modulus of elasticity and strength are hardly relevant for welding but most certainly for the design of structures.
The high electrical conductivity of aluminium may lead to arc striking problems, and the high thermal conductivity to a lack of fusion at the beginning of the weld and to forward-moving welding heat. These aspects are discussed in this article. The high heat conductivity may also lead to overheating of fi xtures and to dimensional deviations, which require a more stable design and probably additional cooling of such devices. In general high heat conductivity and high coeffi cient of expansion give more deviation than compared to steel and must be considered in design and in the construction of welding fi xtures.
Special attention has to be paid to the oxide layer and the solubility of hydrogen.