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To obtain better comprehensive properties of cast Al-Cu-Mg alloys, the secondary aging (T6I6) process (including initial aging, interrupted aging and re-aging stages) was optimized by an orthogonal method. The microstructures of the optimized Al-Cu-Mg alloy were observed by means of scanning electron microscopy and transmission electron microscopy, and the properties were investigated by hardness measurements, tensile tests, exfoliation corrosion tests, and intergranular corrosion tests. Results show that the S phase and θ' phase simultaneously exist in the T6I6 treated alloy. Appropriately increasing the temperature of the interrupted aging in the T6I6 process can improve the mechanical properties and corrosion resistance of Al-Cu-Mg alloy. The optimal comprehensive properties (tensile strength of 443.6 MPa, hardness of 161.6 HV) of the alloy are obtained by initial aging at 180 °C for 2 h, interrupted aging at 90 °C for 30 min, and re-aging at 170 °C for 4 h. [ABSTRACT FROM AUTHOR]

The effect of mechanical properties on wear resistance of Si3N4 - SiC composite materials with different portions of SiC strengthening phase was investigated. Properties of monolithic silicon nitride were compared to ceramic composites consisting of Si3N4 matrix with 10 and 20 vol.% SiC. The SiC strengthening phase had a positive effect on the hardness of Si3N4 - SiC ceramic composite materials. Wear resistance of tested ceramic materials was mainly influenced by their fracture toughness. The highest wear resistance value was achieved for material with the highest fracture toughness. Worn surfaces of all experimental ceramic materials were damaged by both microcutting and microcracking mechanism. Microcracking was the predominant wear mechanism mainly at ceramic composites. The wear resistance of SiC-Si3N4 ceramic composites can be described by the model W ~ HV/KIC.

The effect of mechanical properties on wear resistance of Si3N4 - SiC composite materials with different portions of SiC strengthening phase was investigated. Properties of monolithic silicon nitride were compared to ceramic composites consisting of Si3N4 matrix with 10 and 20 vol.% SiC. The SiC strengthening phase had a positive effect on the hardness of Si3N4 - SiC ceramic composite materials. Wear resistance of tested ceramic materials was mainly influenced by their fracture toughness. The highest wear resistance value was achieved for material with the highest fracture toughness. Worn surfaces of all experimental ceramic materials were damaged by both micro-cutting and microcracking mechanism. Microcracking was the predominant wear mechanism mainly at ceramic composites. The wear resistance of SiC-Si3N4 ceramic composites can be described by the model W ~ HV/KIC [ABSTRACT FROM AUTHOR]