Effect Of Al And Si On Microstruture And Mechanical Properties Of Cu-Ni-Sn Alloy With Low Sn Content

Cu-15Ni-8Sn alloy are excellent elastic material,and have been widely used in aerospace,shipping,electronic components and other industries,with a combination of high strength and toughness,exceptional bearing properties and outstanding corrosion resistance,and excellent anti-stress-relaxation properties,etc.However,it is hardly to avoid severe macro-segregation of Sn during solidification which makes it difficult to produce sheet products when Sn content is high.It weakens the machining performance and mechanical properties of alloy and limits the commercial applications.Therefore,it is a significant research subject of Cu-Ni-Sn alloys to develop low Sn-containing cupronickel alloys with comparable mechanical properties with Cu-15Ni-8Sn alloy.In this work,series of Cu-17Ni-2.5Sn-xAl?x=0,1.5,3?and Cu-9Ni-2.5Sn-1.5Al-xSi?x=0,0.5?alloys was prepared by permanent mold casting,hot extrusion and heating treatment.The effects of addition of Al and Si on the microstructure and properties of hot-extruded alloys have been investigated,and the precipitation behavior of Cu-17Ni-2.5Sn-1.5Al alloy in400?C⁶50?C has been studied.The main conclusions are summarized as follows:?1?In Cu-17Ni-2.5Sn-xAl alloys,the addition of Al results in the precipitation of??-Ni₃Al nanoparticles,which has the relationship with the Cu matrix:[100]??//[200]_Cu,[010]??//[020]_Cuu and[001]??//[001]_Cu.The alloys were effectively strengthened by grain refining,solid solution strengthening and precipitation strengthening.With the increasement of Al content,the tensile strength increased while the elongation decreased gradually.The tensile strength of 1.5Al alloys was 922 MPa,and the elongation was 18%.After hot extrusion,there was a strong<111>fiber texture in the section perpendicular to the extrusion direction,and the texture strength increased with the increasement of Al content.On the interface parallel to the extrusion direction,0Al alloy forms Brass texture{011}<211>and{110}<322>texture.1.5Al alloy is dominated by Goss texture{011}<100>.In addition to strong Goss texture,Cube texture{001}<100>and Copper texture{112}<111>also occur in 3Al alloy.?2?In Cu-9Ni-2.5Sn-1.5Al-xSi alloy,the addition of Si contributes to the precipitation?-Ni₃Si nanoparticles,dispersed in the matrix and with the L1₂ ordering structure,and the relationship of matrix is:[100]?//[200]_Cu,[010]?//[020]_Cu and[001]?//[001]_Cu.The Ni₃Si nanoparticles can effectively inhibit the recrystallization process as well as the grain growth,leading to the bimodal structure consisted of original coarse deformation and recrystallization fine grains of 0.5Si alloy.There is a strong<111>fiber texture in the original deformed microstructure.The addition of Si can significantly strengthen the alloy.The enhanced strength is contributed by:grain refinement strengthening,precipitates strengthening of?-Ni₃Si nanoparticles,texture strengthening in coarse unrecrystallization regions.And the precipitates strengthening play the main role with 67.3%of total strengthening contribution.The tensile strength of 0.5Si alloys was 861 MPa,and the elongation was 18%.In the plane parallel to the extrusion direction,the texture of 0Si alloy is not obvious,and there is weak Brass texture{011}<211>,while 0.5Si alloy has strong P texture{011}<122>.?3?In 400?C⁶50?C aging temperature,only??-Ni₃Al particles were precipitate in Cu-17Ni-2.5Sn-1.5Al alloy.During the early stage of 400?C aging,there is a deviation between[110]??and[220]_Cu.With the increasement of aging temperature and aging time,the relationship between??-Ni₃Al and matrix has formed and keep the relationship of[100]??//[200]_Cu,[010]??//[020]_Cu and[001]??//[002]_Cuu stably.In 400?C⁵50?C aging temperature,the microhardness of matrix is increased with the increasement of aging time and temperature.While,in the aging temperature of 600?C⁶50?C,overage phenomenon has occurred,with the increasement of aging time,the microhardness of alloy is increase at first and then decrease,a hardness peak is existe.