Preparation And Processing Performance Cu-15Ni-28Zn-13Mn-xCo Alloys

A series of new alloys of Cu-15Ni-28Zn-13Mn-xCo(x=0%、0.18%、0.26%、0.51%and0.65%)with high strength were prepared in this study. The relationship of the structure and performance ofalloys with Co content was investigated by physical property measurements, such as hardness andelectric conductivity measurements, tensile strength tests, X-ray diffraction, optical microscopy, andscanning electron microscopy and transmission electron microscopy, and energy spectrum analysis.The influence of Co content on microstructure and properties of alloys were also investigated.Theresults show that:⑴By analysising the thermodynamics and dynamics of the elements oxidation reaction, G﹤0that means the oxidation reactionit is entirely spontaneous reaction during smelting process. Thedynamic process can be divided into two stages: chemical reaction and internal diffusion by thedynamics analysis, the Kinetic formula is1nThe reaction factor R can be reduced by changing tem0p tanderature, timr2⑵The microstructure of alloy as-cast has segregation of Ni and Mn in grains. The grains can berefined with little amount of Co, the increment of grain refinement will slow down when the Cocontent is more than0.51%. The average grain size and small angle grain boundary of the alloywithout Co is109.6μm and0.29respectively. The average grain size and small angle grain boundaryof the alloywith0.26%Co is43.2μm and0.85respectively. The element of Co will be as a core duringsetting process for its high smelting point, so that Co distributes in the internal of grain is more than inthe grain boundary. The hardness of the alloy as-cast with0.51%Co is119Hv which is14.4%higherthan that the alloy without Co (104Hv).⑶With the increase of grain refinement, the specific surface area of grain enhances, and activityenhanced, so that atoms diffuse quickly. The grains volum decreases, so that the segragation areareduces, the diffusion distance of elements shortens，that means the homogenization process is affectedby Co in the alloy, and the homozenazation temperature and holding will be decreased. The reasonablehomogenization condition is750℃×18h for the alloy with Co. The hardness of alloy with0.65%Co by50%thermal deformation is197Hv which is56.3%higher than that alloy without Co (126Hv). Thehardness of alloy with0.65%Co which solid solution treated at800℃×1h is156Hv which is33.3%higher than that alloy without Co (117Hv).⑷The breakage grains by cold-rolling can promote the precipitation of the second phase duringthe aging treatment. β phase of alloy in70%cold deformation preciptes continuously during the agingtreatment, and in the same structure with matrix that is good for of ageing strengthening. The tensilestrength and elongation of the alloy with0.65%Co in70%deformation is922MPa and3.5% respectively that is5.4%and25%higher respectively than that alloy without Co (875MPa and2.8%).The tensile strength and elongation of the alloy with0.65%Co aging treated at400℃×8h aftercold-rolled is1140MPa and3.8%respectively that is22.7%and4.4%higher respectively than thatalloy without Co (929MPa and3.64%). The β phase diffusion is more homogenization with theincrease of aging time, so that the density of toughness nests of tensile fracture increases and theductility enhances.