The Tribological Properties of Cast Zinc-Graphite Composite

In order to improve the friction behavior and to extend the application range, the high aluminum Zinc-based alloy ZA-27 (Zn-27%Al-2%Cu-0.02%Mg) is used for matrix. The Zinc-based alloy is compounded with graphite into homogeneous slurry under the melting state by means of the pretreattnent of graphite, mechanical stirring and alloying technique, and then the slurry is squeezed under 70-100 MPa to take shape to obtain the Zinc-graphite composite cast. The microstructure analysis shown that the integrating state of interface between graphite and metal is good. The soft graphite phase is well-distributed in the hard metal matrix. Since the action of pressure the graphite is squeezed out to form a continuous lubricating film on the friction surface during sliding friction condition. This film protects the metal surface from the contact and influences the friction properties. The SEM results of friction surface shown that the friction surfaces of ZA-27 alloy without graphite appear the deeper furrows and adhesive wear scars, whereas the friction surfaces of Zinc-graphite composite present uniform wear even under the unlubricated condition. Zinc-graphite composite in which graphite content is less than 6 % (wt) still retains higher load carrying capacity than bronze ZQSnG-6-3. The linear expansion coefficient decreases with the increasing of graphite content. When the graphite content is 10% the linear expansion coefficient decreases approximate 10%, and the composite displays the excellent friction properties. Within the given range of graphite content of this test, with the increasing of graphite content the duration required for wear to reach the steady state decreases in the friction course, the smoothness of the sliding course increases, the temperature of friction surface drops, the wear becomes uniform, the wear rate and friction coefficient decreases. When the graphite content is 6%, the antifriction, antiwear and relative seizure resistance properties of Zinc-graphite composite show 2.87, 2.81 and 3.0 fold increase over those of matrix alloy respectively. The results suggested that the Zinc-graphite composite has the vast prospect as a new antifriction and antiwear material.