【摘要】 连续挤压流动的均匀性关系到板材组织的均匀性。本文采用630型连续挤压机，以直径为30 mm铜杆为原料，分别经U型模式和平板型模式挤压出420 mm×15.5 mm和235 mm×15 mm铜板材。结合金相显微镜（OM）、扫描电子显微镜（SEM）、硬度计、拉伸试验机以及HyperXtrude软件，研究了两种铜板材的显微组织和力学性能，并模拟计算了两种挤压模式的流动特点。结果表明：U型连续挤压成形板材晶粒尺寸范围为20～100μm，平板型连续挤压板材的晶粒尺寸范围为8～200μm；根据板材上、中、下层的各向异性系数对比，U型连续挤压板材的各向同性优于平板型连续挤压板材；U型板材硬度相对偏差小于平板型连续挤压板材。U型连续挤压板材良好的组织结构和力学性能，缘于在模腔中各点金属的流动距离偏差小，流速均匀，使各区域的晶粒尺寸变化范围小。相对而言，平板型连续挤压模腔中部区域与边部区域金属的流动距离差别较大，流速均匀性差，造成板材各区域晶粒尺寸的不均匀性增加。更多还原

【Abstract】 The use of continuous extrusion technology to produce copper sheets have the advantages of energy conservation and efficiency compared to rolling processes. However, due to the limitations of continuous extrusion flow characteristics, as the width of continuous extrusion expansion increases, the extrusion force increases exponentially. At the same time, the non-uniformity of metal flow increases, exacerbating the non-uniformity of sheet microstructure and properties, making it difficult for the current continuous extrusion copper sheet to exceed a width of 320 mm. To solve this problem, in 2017, a U-shaped continuous extrusion process was proposed, which changed the traditional flat continuous extrusion mode of extruding flat sheets to extruding U-shaped sheets. This could increase the expansion width to 420 mm. The U-shaped extrusion process significantly reduced the extrusion load while also improving the uniformity of flow. It is very necessary for the application of U-shaped continuous extrusion technology to be clarified what are the differences in microstructure and properties between U-shaped copper sheets and flat sheets. The sheets with a cross-section of 420 mm×15.5 mm was obtained by U-shaped continuous extrusion and the sheets with a cross-section of 235 mm×15 mm by flat continuous extrusion. Both copper sheets were produced by 630-type continuous extrusion machine. A pure copper rod with a diameter of 30 mm was used as the blank material. The microstructure and mechanical properties of two kinds of copper sheets were studied by optical microscope, microhardness tester, and tensile testing machine. The flow characteristics of both extrusion modes were simulated by HyperXtrude software. The results showed that the microstructure of copper sheets of U-shaped continuous extrusion had equiaxed and twin crystal structures. There was no significant difference in grain size from the central region to the edge region, from the upper and middle zone to the lower zone. The grain size of the U-shaped copper sheet was 20～100 μm, and the average grain size difference between the central and edge region was 1 μm. The flow velocity in the central region of flat continuous extrusion sheets was high, which made partial grain size small and grain boundary bending.In the edge region of the sheet, the flow path was long and the flow velocity was low, which increased grain size and grain boundary flattening. The grain size of the flat copper sheet was 8～200 μm, and the average grain size difference between the central and edge region was 5 μm. Finite element simulation results indicated that standard deviation of velocity(SDV) of U-shaped continuous extrusion was 1.15and that of flat continuous extrusion was 6.54. The flow uniformity of U-shaped continuous extrusion was better than that of flat continuous extrusion. The mechanical properties of copper sheets produced by the two methods were relatively consistent. The difference in tensile strength at the same position of the sheets did not exceed 20 MPa and percentage elongation was above 45%. A large number of dimples with ductile fracture characteristics were distributed in the fracture surfaces of the two types of sheets. It showed that they all had good plasticity. The subtraction between the ratio of transverse and longitudinal strength-elongation product and 1.0 could be defined as the anisotropic coefficient. The closer the value approached zero, the smaller the difference in the anisotropy of the sheets. By comparing the anisotropy coefficients of the central and edge regions of the sheet, as well as the upper, middle, and lower zones, it was shown that the U-shaped continuous extrusion sheet had good isotropy. The hardness test indicated that the hardness range of U-shaped sheets was HV 67～78, and the hardness range of flat sheets was HV 60～75, the overall hardness of U-shaped was greater than that of flat. The relative hardness deviation of the U-shaped sheet was less than the result of the flat sheet. The U-shaped sheet had better subsequent processing performance. The copper sheets of U-shaped continuous extrusion had good microstructure and mechanical properties. They were mainly attributed to the small deviation of the flow distance at each point in the cavity.The uniform flow velocity and plastic deformationled to insignificant changes in the degree of recrystallization at various locations. During the expansion process of flat continuous extrusion, the flow distance of metal in the middle region of the cavity was different from that in the edge region, resulting in a fast flow velocity in the central region and a slow flow velocity in the edge region. Although the strain in the edge region was large, the extension of residence time in the cavity played a dominant role in grain change, which caused performance differences between the central and edge regions of the sheet.更多还原