Mechanical And Tribological Properties Of Aluminum Bronze Alloy Produced By Equal Channel Angular Extrusion

As a kind of excellent engineering materials, aluminum bronze alloys are widely used under high stress condition due to their outstanding physical, mechanical, wear-resistance and anti-corrosion properties. Many studies have been carried out on tribological properties of aluminum bronze alloys since 1980's. Most of these studies focused on the improvement of tribological properties by changing the composition and volume of microelements in the alloys. However, this method has its own limitation and can not obviously improve tribological properties of aluminum bronze alloys. In practice, many modern aluminum bronze components require high strength and low friction and wear, therefore, there is an urgent necessary to largely improve mechanical properties and wear resistance of aluminum bronze alloys by new technique.Equal channel angular extrusion (ECAE) technique is a severe plastic deformation process which can produce bulk ultra fine-grained materials by simple shear. One important advantage of ECAE is that it imposes very high plastic strain on alloys during pressing, which results in unique combinations of mechanical properties and grain size of alloys. In this study, in view of microstructure is a key factor which influences the performance of aluminum bronze alloy, and machining characteristic of the alloy is poor at a low temperature, an advanced equal channel angular extrusion technology has been used to process aluminum bronze alloy (QAl9-4) in order to refine the microstructure, and then improve the mechanical and tribological properties of aluminum bronze alloy. Some significant original results have been obtained.Firstly, high temperature ECAE processing was used for the microstructural refinement of aluminum bronze alloy, the effects of preheating temperature, friction, extrusion numbers and annealing treatment on the microstructure of aluminum bronze alloy were analyzed by optical microstructure photographs, and process variables were determined. The microstructural refinement mechanism produced by high temperature ECAE processing was also discussed. The results showed that the grain size of the aluminum bronze alloy decreased with the increase of pass number. Recrystallization occurred and the grain size was further refined after annealing treatment at 500℃.Secondly, the effects of high temperature ECAE processing on hardness and mechanical properties of the aluminum bronze alloy were analyzed, and the mechanism of ECAE for the improvement of mechanical properties was discussed. The results showed that the hardness and yield strength of aluminum bronze alloy increased with the increase of pass number. The improvement of hardness and mechanical properties of the alloy after ECAE was mainly due to grain refinement.Thirdly, the effects of high temperature ECAE processing on the second phase of aluminum bronze alloy were analyzed. The results showed that the second phase was refined and distributed dispersedly in the matrix of the alloy after ECAE. The refined particles could cut the soft matrix, which was useful to grain refinement during ECAE. The dispersoid distribution of the second phase could strengthen the matrix and improve mechanical properties of the alloy.Fourthly, the tribological properties and wear behaviors of aluminum bronze alloy under both dry sliding and oil-lubricated conditions were investigated in detail. The results showed that the tribological properties of aluminum bronze alloy were greatly improved by high temperature ECAE processing. The aluminum bronze alloy treated by high temperature ECAE processing registered the better tribological properties than untreated alloy. Under low load condition, abrasive wear was the main wear mechanism for the untreated and treated alloy. The depth and width of the furrows decreased with the increase of pass number. Under high load condition, heavy abrasive wear was the main wear mechanism for the untreated alloy, while abrasive wear of the alloys treated by ECAE was decreased after ECAE. Under oil-lubricated condition, the direct contact of the friction pair was reduced by the oil film. The friction heat was carried away by oil, resulting in a great decrease in plowing. The wear mechanism of the aluminum bronze alloy under oil-lubricated condition was slight abrasive wear.Fifthly, the mechanism of the influence of high temperature ECAE processing on the tribological properties of the aluminum bronze alloy was discussed. The microstructure and the second phase of the aluminum bronze were refined after ECAE. The dispersoid distribution of the second phase could strengthen the surface of the alloy, which decreased the quantity of abrasive particles. The wear volume of the alloy was decreased. The hardness and strength of the alloy were increased after ECAE. The resistance of deformation was improved and the depth and width of furrows were decreased due to the increase of hardness and strength. As a result, the wear-resistance and tribological properties of the alloy were improved after ECAE.It is the first efforts to use high temperature ECAE processing for aluminum bronze alloy, and investigate the influence of high temperature ECAE processing on the microstructure of the aluminum bronze alloy. The interrelationship between the microstructure and mechanical properties of the alloy was obtained. The effects of microstructure, mechanical properties, load and sliding speed on friction and wear behaviors of aluminum bronze alloy under both dry sliding and oil-lubricated conditions were investigated in detail. The wear mechanism of aluminum bronze alloy treated by ECAE was analyzed. This study is promising to improve the properties and applications of aluminum bronze alloy.