| In this paper, hypoeutectic Cu-l.OCr in-situ composites wires were prepared perfectly by continuous unidirectional solidification & heated-mould continuous casting method. Selection and effect of solidification parameters on the surface quality of Cu-l.OCr in-situ composites wire were discussed. The properties of microstructure characteristics , morphology evolution and mechanism of two phases growth in the normal solidification samples and continuous casting samples were researched and compared, by means of optical microscope(OM), Scanning Electron Microscopy (SEM) , X-ray Diffraction (XRD) and image analysis technique etc, and relationship of parameters and microstructure was established. Mechanical property of under room temperature was tested , and fracture characteristics and fracture mechanism were researched;Electric resistance of continuous casting sample is tested with microhmmeter and the relationship between solidification processing controlling and the essence of conductivity was analyzed for Cu-Cr in-situ composites wire. The main subjects and conclusions are as follows:The optimal parameters were obtained by theoretical analyse and practical operation , and the sample with good surface quality was prepared with the optical parameters. In this test, there was a solid-liquid mixing zone (pasty zone) in the front of the mould because of broad field of temperature for hypoeutectic Cu-Cr alloys solidification. It's important to control the position of liquid phase interface and solid phase interface of the zone for surface quality of the bar. In the processing, some defects appeared on the surface of the wire such as crack, cold lap, axial groove, caving wave, abruption etc .These defects could be slaked by adjusting the parameters.It's found that the microstructures of the hypoeutectic Cu-1.0%Cr in-situ composite were made up of primary a phase and eutectic (a+P), which arrayed by each other and regular along the directional orientation as long or short fiber forms. The microstructures grew along the (200) crystal plane with [100] orientation after themicrostructure's evolution. The primary a phase underwent a series of change from plane front, cystiform, cystiform & dendrite, thick dendrite to thin dendrite after rate is steady , with the increase of solidification rates and the interface morphology evolution . The 1st dendrite space (A4) is increasing initially and then reducing with solidification rates increasing , whose dimension is answered for "bifurcation" and " submersion" mode, but eutectic content always reduces. Not only thermal field, solute distribution and space of the front edge for solidification but also the primary a phase have effects on eutectic (a+p) growth. There was the maximal aliquation of Cr, normal segregation , which reduce with the solidification rates creasing. (P-Cr) phase is formed from eutectic reaction . (P-Cr) phase play a role of strengthening together with the primary a phase of the eutectic.The samples of continuous casting have good plastic property , strength, and less yield ratio, which increase with the solidification rates increasing, and good ability of secondary machining. There is no change of fracture form but the size because of the solidification rates changing. Lots of toughness nests lie in the nick, which are connected each other by tearing edges and become uniform ,smaller, dense, directional with the solidification rates increasing. It is found that there are more glide lines and the second cracks on the inwall of toughness nests. Sliding is the major factor of the sample's deforming, but surface turning appear close to the field of failure. The conductivity of continuous casting is better because there are less transverse crystal boundary ,smooth and straight microstructures and no cavity and inner vesicle in the sample, in fact, the optimal parameters and processes are effective on the conductivity of the continuous casting bar. |
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