MICROSTRUCTURE AND PROPERTIES OF 7475 ALUMINIUM ALLOY MATRIX NANO-COMPOSITES WITH 10-20% Al2O3 OR AlN ADDITIONS

The microstructure and properties of two types of 7475 aluminium alloy matrix composites -with additions of 10 divided by 20 wt.% of nano-Al2O3 or AlN (<40 mu m) were investigated. The composites were produced through powder-metallurgy processing. Pre-alloyed 7475 aluminium powders were mixed with ceramic particles and milled in a high energy planetary Fritsch ball mill for up to 40 hours. Next, they were compacted at 380 degrees C and 600 MPa. The microstructure of the obtained composites was studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The performed investigations proved that both types of composites show a good dispersion of ceramic phases. The composite matrix was characterized by a fine grain size, i.e. less than 100 nm and contained a high density of intermetallic, Zn, Cu or Fe rich phases. The EDX chemical analysis indicated the local presence of an MgO phase at the metal/Al2O3 and metal/AlN interfaces. The microhardness of the compacts were in the range of 315 divided by 355 HV and 250 divided by 280 HV range for composites with micro-AlN or nano-Al2O3, respectively. It indicates that the size of the nano-crystalline matrix and intermetalic precipitates play a more important role than that of the reinforcing ceramic particles.