| In this paper, casting ternary alloy CuAlMn alloy was selected as the research object. As-casting microstructure, as-martensite microstructure, shape memory property, mechical property, transformation property and cold working property of 4 groups alloys with different contents of Al and Mn alloy 1#Cu-8.7Al-7.1Mn, 2#Cu-8.5A1-12Mn,3#Cu-12.3A1-5.4Mn and 4#Cu-10.2Al-8.5Mn and 4# alloy with 0.1-0.4wt.% contents of rare earth La was studied by OM, SEM+EDS, TEM+EDX, XRD, DSC, tensile test, bending test and cold rolling test. The results show that:There is a large number of a phase precipitated in 1# alloy for its low Al content, which caused almost no memory property for 1# alloy. By increasing the content of Mn, the percent of martensite has increased, but it still can’t form single martensite phase, the memory property is only 42%. Therefore, prepared 1# and 2# alloy has no practical value.3# alloy with high Al and low Mn content has single martensitic phase, the transformation thermal hysteresis temperature is only 6.6℃, the memory property is excellent up to 99.7%, but the fracture elongation is only 7.5% and cold working property is less than 10%, which is not suitable for cold working. Besides, the grain size is coarse. The fracture elongation of 4# alloy reaches to 12.8%, the maximum cold working poperty reaches to 30%, which is 3 times of 3# alloy’s. But the decreasing of Al content leads to the decreasing of the order degree of the alloy. So the transformation thermal hysteresis temperature is 18.5℃, and the shape memory property is 91.3%.For 4# alloy addition with 0.1%,0.2%,0.3% and 0.4% rare earth La, the amount of La-rich precipitates increase with the increasing of La contents, at the same time, the grain size of casting alloy decreases. The La-rich precipitates can inhibit the extension of grain boundary during heat treatment, so refining the matensite grains and improving the consistency of martensite variants. In the d# alloy with 0.3% La addition, the casting grain size and matensite grain size both reached the minimum. But the casting and matensite grain refinement effect becomes worse for the e# alloy with 0.4% La addition, the grain boundary becomes blurred, and the martensite order degree decreases. When the content of La is lower, the more of La content, the better of the memory property. Memory property of d# alloy with 0.3% La addition reaches the maximum value 95.6%. But e# alloy decerases the order degree of martensite for formation large number of aggregation La-rich precipitation, which caused the memory property, which is only 85%. aggregation La-rich precipitation, which caused the memory property, which is only 85%.With the addition of La, the alloy liquid become purification, impurity contents decreased, the grain size become smaller, and the tensile strength, elongation and cold working property become better. These properties become to the maximum when 0.3% La addition. But 0.4% La addition destroied the continuity of the microstructure for the formation of a large number of continuous precipitates, which is useless to improve the properties of alloy.SEM and TEM results show that approximately 1μm circular-like La-rich precipitates formed in the CuA1Mn alloy with the addition of rare earth element La. XRD results show that the La-rich precipitates is similar with a phase, and they are solid solution that La, A1 and Mn dissolved in Cu, their melting point is high and property is stable. The La-rich phases were precipitated at the grain boundaries mainly, which increases the strength of grain boundaries, thus improving the mechanical properties of the alloy.Addition 0.3% La in ductile Cu-10.2A1-8.5Mn alloy can refine the matensite grain size to only 68.1 μm. At the same time, a better order degree of martensite can be obtained. The memory property reaches to 95.6%, tensile strength and elongation reaches 777.1MPa and 17.6% respectively, and cold working property is 48%. Alloy with this composition can solve the contradiction between the high memory performance and the low cold working performance of copper-based memory alloy. |
PDF Full Text Request