Study On Microstructure And Properties Of Tin Bronze Prepared By Centrifugal Casting

The low strength and hardness of copper bushing in heavy load environment often causes the phenomenon of copper bushing and friction pair biting to death.In this study,by designing Cu-Sn alloy as the base and adding trace Ni,P,Be elements,Cu-Sn-Ni-P-Be alloy was prepared through centrifugal casting,and the heat treatment was carried out to improve the strength and hardness of the alloy,and then improve the wear resistance of the alloy.The hardness of the alloy was measured by Brinell hardness tester,and the tensile strength of the alloy was measured by universal tester.The microstructure of the alloy was observed by optical microscope（OM）,the friction and wear tests were carried out on the alloy,and the friction and wear morphology was observed by emission scanning electron microscope（FE-SEM）.X-ray diffraction（XRD）and transmission electron microscopy（TEM）were used to study the precipitates and reveal the strengthening mechanism of the alloy.The OCP,EIS and polarization curves of the alloy were measured by electrochemical workstation.The corrosion products were characterized by XRD,SEM and EDS and the reaction mechanism was revealed.After aging at 430℃×2h,the hardness,tensile strength and elongation of Cu-Sn-Ni-P-Be alloy can reach 144.3HB,362.08MPa and 5.18%respectively.The reason is that ellipsoidal and disc-like phases（Ni Be phase）can precipitate in the matrix after aging,which exists a cogrid orientation relationship withα-Cu matrix:（11 0）_γ′//（200）_α.After solution treatment at 780℃×1h and aging treatment at 430℃,the first peak of hardness 180.7HB appears at 0.5h,meanwhile the tensile strength of the alloy reaches531.82MPa and the elongation is 4.98%.The precipitates are disk-shaped,having a co-lattice relationship with theα-Cu matrix:（01 1）_γ′//（11 1）_α.However,after aging for 4h,the second peak hardness of the alloy reaches 175HB,which is mainly attributed to the formation of acicular D0₃ phase,namelyγphase,resulting in the tensile strength of the alloy decreasing to 308.50MPa,while its elongation is only 3.48%.At room temperature of 20℃,the COF of the solution aged alloy is higher than that of the direct aged alloy,and the COF of the direct aged alloy is higher than that of the cast alloy.The wear of the solution aged alloy is lower than that of the direct aged alloy,and the wear of the direct aged alloy is lower than that of the cast alloy.The wear mechanism of the alloy in the heat treatment state is mainly abrasive wear,accompanied by certain delamination wear and adhesive wear.At the high temperature of 200℃,the wear mechanism of each heat treated alloy is mainly oxidized wear and adhesive wear.At the high temperature of 400℃,the main wear mechanisms are oxidation wear and abrasive wear.According to the comparison of E_corr,I_corr,R_ct and Z_W,the corrosion resistance is as follows:solid solution state<direct-aging state<as-cast state<solid solution aging state.The corrosion resistance of the solid solution alloy is the worst.The corrosion products contain Cu O or Cu₂（OH）₃Cl,implying obvious pitting corrosion occurs.The corrosion resistance of 430℃×2h alloy is inferior to that of the cast alloy,because the precipitate with small size can be used as a channel to further accelerate pitting corrosion,but it will also isolate foreign oxygen and inhibit its oxidation when the depth of pitting corrosion is increased.The 780℃×1h+430℃×4h alloy has the best corrosion resistance,and its corrosion products only contain Cu Cl and Cu₂O,but no Cu O or Cu₂（OH）₃Cl.This is because D0₃ phase precipitated near the grain boundary during aging increases the electrode potential at the grain boundary,thus reducing the corrosion rate of the alloy.