中文摘要：

提出了金属梯度结构轴的概念．研究了固－液复合的25Cr5MoA钢／Q235钢复合轴的组织、Cr元素的扩散以及结合界面附近显微硬度的变化规律．结果表明：经过挤压变形后，25Cr5MoA钢／Q235钢界面形成了良好的冶金结合，二者结合紧密，除了组织结构的差别外，二者的结合界面已经难以区分．结合界面附近Cr元素在固-液复合时得到充分扩散，并呈现出连续分布的形态．从界面向Q235钢和25Cr5MoA钢两侧±100μm范围内，硬度呈现出均匀、连续分布．经过热处理后，随着加热温度的升高和加热时间的延长，Cr元素在结合界面附近的分布更加均匀，分布曲线在界面的斜率进一步降低，使结合界面附近25Cr5MoA钢的一侧的显微硬度大幅度降低，这有利于形成化学成分、组织以及性能的梯度变化．

英文摘要：

The concept of metal gradient structure shafts was put forward firstly. The microstructure, diffusion behavior of Cr element, and variation in interracial microhardness of a 25CrSMoA/Q235 clad shaft prepared by solid-liquid cladding were investigated by scanning electron microscope and microhardness tester. The bonding interface of the 25CrSMoA/Q235 cladding shaft forms close metallurgical bonding after extrusion deformation, and it is difficult to be identified except the difference of individual structure. Cr element in a region adjacent to the bonding interface is fully diffusive and appears continuous distribution during solid-liquid bonding. Across a region ranging from the bonding interface to both sides by the distance of 100μm respectively, the microhardness distributes continuously and uniformly. Additionally, during heat treatment, increasing the heating temperature and holding time makes Cr distribution in a region adjacent to the bonding interface more uniform and the slope rate of Cr distribution curves at the bonding interface reduced more, which greatly reduce the microhardness at the 25CrSMoA side adjacent to the bonding interface. It is advantageous to form gradient variations in chemical composition, structure and mechanical properties at a region across the bonding interface.