Microstructural evaluation of solid state welds obtained by means of flat rolling process

In extrusion operations based on the use of porthole dies, for the fabrication of tubes and hollow profiles in general, material solid state welding takes place thanks to the very high pressure and temperature at which the material undergoes. Nevertheless, the most important aspect in this process still remains the quality of the welds, also because the testing of extruded tubes is still today an un-regulated matter. A technique based on the flat rolling process is applied in this paper, in combination with micrographic and macrographic analyses, to assess the quality of solid-state welds obtained using different process conditions. Flat rolling experimental tests executed on sandwiches made of two rectangular specimens in AA6060 and AA6082 aluminium alloys were performed. The specimens were characterized by different heights in order to consider different compression ratios that mean different interface pressure and effective stress distributions. All the tests were repeated at different temperature. By verifying if, the material bonding took place or not, it was possible to identify the welding limits conditions in terms of pressure and temperature. Particular attention was paid to the study of both the macrostructure and microstructure of the rolled specimens in order to identify the influence of the process parameters on both the material weldability and the metallurgical weld quality.