Microstructure and X-Ray Diffraction analysis of Al-Cu Couples Diffused at High Temperature

By employing a thermal field of 813 K, couples of Al with Cu were welded as consequence of the atomic diffusion. The periods of permanency inside the field were 200, 320 and 480 hours. After the periods of test, SEM observations show the formation of two contiguous plate likes (similar to 15 to 30 micrometres, width) that they are in normal position to the concentration gradient. By utilizing elemental analyses and X-ray diffraction techniques one plate like was identified as the eta 2phase (CuAl) and the other one as the theta phase (CuAl2) of the aluminium-copper system. Immediate to the theta plate like it is expanded a zone formed by irregular theta grains surrounded by a network of alpha Al. Finally, far from the welding line, the saturated theta grains decompose and transform into pearlite according to the reaction alpha Al + theta -> alpha Al + alpha Cu.