TWI Industrial Member Report Summary 776/2003
M F Gittos and K Bridges
Aluminium alloys containing scandium have received a great deal of attention recently, due to claims that the addition of small amounts of scandium can improve weldability, increase strength and raise recrystallisation temperatures.
The mechanism of grain refinement is by the formation of Al3Sc particles in the melt. Fine coherent Al3Sc precipitates also form in the solid state and have a profound effect in inhibiting recrystallisation.
Although there are a number of 'commercially' available Russian alloys which contain scandium, the amount of published material which substantiates the various attractive claims as to the benefits of alloying with this transition metal, remain few. However, it is unlikely that all of the quoted benefits, such as reduced weld porosity, can be attributed to the grain refining effects which have been shown to occur.
This report assesses the effects of low level scandium additions to two 7XXX alloys with respect to TIG and friction stir welds made in 2.5 and 6mm thick sheets.
- To characterise the microstructure of friction stir welds and arc welds in Sc-containing alloys.
- To compare solidification crack susceptibility of weld metal with and without scandium.
- To determine the mechanical properties of TIG and friction stir welds in similar scandium and non-scandium-containing alloys.