A first step towards the development of self-healing aluminium alloys by friction stir processing

The aim of this master thesis is to fabricate a metal matrix composite (MMC) by using the Friction Stir Processing (FSP) in order to obtain a material system with the ability of mitigating crack damages by post treatments. In order to reach the required system, Al 6063 alloy was chosen and used as the base material and pure Mg was added to obtain the desired microstructure. Mg strip was placed on a groove made on the Al 6063 plate and by FSP a uniform nugget containing Mg-rich particles was obtained. Optimized processing parameters were obtained for FSP and using 16 passes lead to have the highest distribution of particles in the nugget. Regarding the mechanical properties of the material system, micro hardness and nano-indentation results show that addition of Mg and formation of well-distributed Mg-rich particles go in hand with an increase in the strength and modules of the alloy. In addition, interrupted notch tensile test at maximum force revealed that sample containing Mg-rich particles has a higher strength comparing to the FSPed sample without addition of Mg. In order to identify damage mechanism of the FSPed samples two different approaches were performed. At first, the highly damaged sample after interrupted notch tensile test was analyzed by scanning electron microscopy (SEM). Furthermore, another sample containing Mg-rich particles was analyzed under in-situ SEM tensile test. Both approaches reveal that instead of unwanted crack formation over hard Fe-rich intermetallics, cracks were formed close to Mg-rich particles. Heat-treatment of the sample was performed on the highly damaged sample to possibly reach an optimized healing cycle of cracks in the microstructure by partial melting of the Mg-rich particles