Cu基超弹性合金的冷变形能力研究

【作者】 于能；

【导师】 黎沃光；

【作者基本信息】 广东工业大学 ， 材料加工工程， 2007， 硕士

【摘要】 Cu基形状记忆合金的冷加工能力较差，目前多数的研究工作都集中在细化晶粒，使应力集中分散，以改善Cu基合金的延性和疲劳性能。同时也有众多的研究者正试图找到冷变形能力较好的新型Cu基合金以推动其实用化进程。本课题对新型Cu-Al-Mn和Cu-Al-Be合金的冷变形能力进行了研究，并使用热型连铸法定向凝固以得到粗大的柱状晶组织，通过强化织构来提高Cu基合金的力学性能和疲劳性能。同时尝试了增加Ni元素的方法以提高Cu-Al-Mn合金的冷变形能力。采用水平式热型连铸装置在拉铸速度为200mm／min时制得Cu-Al-Mn以及Cu-Al-Be超弹性合金丝。在室温下作拉伸试验，以测定Cu-Al-Mn和Cu-Al-Be合金丝的抗拉强度和延伸率；用自制的弯曲疲劳试验机，测定了Cu-Al-Be合金的弯曲疲劳寿命；用DSC法测试了Cu-Al-Be合金的相变温度；用X-射线衍射仪分析了Cu-Al-Mn以及Cu-Al-Be合金；并用金相显微镜观察合金在铸态、热处理后的组织形态。研究结果表明：用热型连铸法拉铸的Cu-Al-Mn和Cu-Al-Be合金都能获得柱状晶粒。铸态Cu-Al-Mn合金在800℃固溶15min后再在550℃下保温60min，淬水，这时合金组织发生了有序→无序转变，并由β相基体析出较大的α相颗粒，合金的最大冷轧变形量由铸态的4.2％升高到8％，同时合金的最大拉伸应变量升高为6.3％。变形后合金在250℃、350℃、450℃温度下进行热处理实验，并不能完全消除马氏体，550℃时则出现等轴晶。Ni元素的添加也不能有效提高Cu-Al-Mn合金的冷加工性能。Cu-Al-Be合金具有极好的冷变形能力，铸态时最大冷轧变形量可达40％，最大拉伸应变量为47％，并且最大弹性应变量不低于10％；700℃保温5min，空冷后合金的最大拉伸应变量更是超过50％；而750℃保温15min，淬水，200℃保温15h热处理后的合金因为γ₂相的析出，使得最大拉伸应变量下降到19％，并且在约6％的应变量时就已经出现2.5％的残余应变。变形量为0.2mm的Cu-Al-Be合金在650℃、700℃保温30s后可以完全消除应力诱发马氏体，并可进行二次变形。铸态Cu-Al-Be合金具有良好的疲劳性能，在应变量为6％时的弯曲疲劳寿命可达45283次，经700℃保温5min热处理后合金的弯曲疲劳次数可进一步提高。更多还原

【Abstract】 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.更多还原