Cold Deformation Capacity Of Cu-based Super-elastic Alloys

The cold-workability ability of Cu based SMA was very low. At present, mostresearches focus on grain refinement, which can disperse the stress concentration, inorder to improve the ductile and fatigue properties. Lots of researcher were trying tolook for alloy that with excellent cold-deformation ability at the same time. Thepurpose of this experiment was to study the new Cu-Al-Mn and Cu-Al-Be alloy'sability of cold-deformation, and improve mechanical properties and super elasticity ofthis two alloy by strengthening texture, obtaining a longitudinal columnar structure byheated mold continuous casting process. The accretion of Ni was tried to improve thecold-deformation ability of Cu-Al-Mn alloys at the same time.Cu-Al-Mn and Cu-Al-Be SE alloy wires are cast by heated mold continuouscasting process at 200mm/min casting speeds. The tensile strength, elongation rate oftwo alloy are measured with tensile experiment equipment at room temperature; Therepeat bending fatigue life of Cu-Al-Be alloy wires is determined by a self-designedequipment; The character phase transformation temperatures of Cu-Al-Be alloy weremeasured by Digital Scan Calorimeter (DSC); Cu-Al-Mn and Cu-Al-Be alloy wireswere analyzed with X-ray Diffraction (XRD); The structure of alloy as-cast and afterheat-treated were observed by metallography microscope.The result shows that: the Cu-Al-Mn and Cu-Al-Be alloy wires cast by heatedmold continuous casting process can get columnar grain structure. The order-disordertransition was happened, and the massiveαphases precipitated in theβphases, thedeformation rate of alloy increase from 4.2% just at as-cast up to 8%; and theelongation rate up to 6.3% after solution treatment at 800℃for 15min, followed byholding at 550℃for 60min, quenching. The martensite of alloy after deformed can't beremoved fully when being heat-treated at 250℃,350℃,450℃, the alloy appearequl-axle grain at 550℃. The accretion of Ni can't improve alloys' cold-deformationabilities effective yet.Cu-Al-Be alloy have excellent cold-deformation ability just at as-cast. It'smaximum deformation rate was up to 40%, and the elongation rate up to 47%, the elastic strain exceeds 10% also; It's maximum elongation rate exceed 50% after heat-treatment at 700℃for 5min; the elongation rate of alloy was only 19%, and 2.5% ofthem was remained after unloaded in 6% elongation rate, because of the precipitationofγ₂ after heat-treated at 750℃holding for 15min, quenching, aging for 15h at 200℃.Cu-Al-Be alloy under 0.2mm deformation rate can remove martensite entirely,and can fulfill secondary deformation.Cu-Al-Be alloy have excellent bending fatigue property just at as-cast, thebending fatigue lifetime reaches 45283 cycles in 6% bending stain, and the bendingfatigue lifetime are improve further after heat-treated at 700℃for 5min.