Microstructure and mechanical properties of aa7475/AlN compacts with varied reinforcing particles size
Marta Gajewska, Jan Dutkiewicz, Jerzy Morgiel
Quarterly No. 3, 2012 pages 177-181
DOI:
keywords: metal matrix composites, aluminium alloy matrix, 7475/AlN, powder metallurgy
abstract The microstructure and properties of 7475 aluminium alloy matrix composites - with additions of 10 wt. % of AlN powders of different particle size: < 40 μm, ~1μ m and < 1 μm were investigated. The composites were produced by means of powder-metallurgy. Pre-alloyed 7475 aluminium powders were milled with ceramic particles in a high energy planetary Fritsch ball mill for up to 40 hours and subsequently vacuum hot pressed at 380°C and 600 MPa. The microstructure of the obtained composites was studied using a metallographic microscope and scanning electron microscope (SEM). The performed investigations indicated good dispersion of ceramic phases. However, in the composite with the submicron AlN addition, a small tendency for agglomeration occurred. All of the composites were characterized by high density of intermetallic, Zn, Cu, Mg or Fe rich phases. Recrystallized Al grains were observed in the composite with the submicron AlN addition, indicating that the fine particles did not retard grain boundaries movement. The hardness of the consolidated samples was highest for the ~1 μm ceramic powder addition - nearly 320 HV in comparison to 250 HV for the finer powder addition. The compression tests showed 830 MPa of ultimate compression strength of the samples with the ~1 μm AlN particles, which was slightly higher than that with the submicron particles addition. The higher strength of the composites reinforced with the micro- rather than with submicro-particles suggests that the size of the ceramic phase addition can be considered as only one of the factors influencing the composite strength.