INFLUENCE OF HEAT TREATMENT PARAMETERS ON THE METALLURGICAL QUALITY OF EN AW 7068 EXTRUDED BARS

摘要

In the present research activity EN AW 7068 alloy samples have been analyzed, from morphological and mechanical point of view. Extrusion process has been employed for the alloy production. As industrial routine, following the manufacturing the alloy has been submitted to different thermal treatments. Thermal treated samples have been extracted by cutting procedures and the obtained samples, have been submitted to standard laboratory preparation and then to morphological and mechanical characterization. Some preliminary SEM analysis reveal the presence of secondary particles. The secondary phase grains are mostly uniformly distributed in both longitudinal and transverse sections. Moreover, especially in the longitudinal section, the grains appear organized along parallel lines to the extrusion direction. According to the EDS analysis results these particles are prevalently made of Al, Cu, Zn and Mg. With the goal to achieve the dissolution of Cu-rich phases, two new solution heat treatments were performed at 470°C for 48 h and at 470°C for 24 h. Effectively, the new solution heat treatments have allowed to reach the dissolution of Cu-rich phases and secondly allowed to obtain a more homogeneous microstructure, especially for as regard the microstructure of cross section. So these thermal treatments could be adopted to dissolve Cu-rich phases that are deleterious for the mechanical properties.