轧制镀工艺

1.轧制镀的提出

粉末轧制镀( plating powder and oling method)全称为金属粉末一板带复合轧制镀，英文缩写为PPR法，是昆明理工大学在20世纪90年代研究开发的-项制备双金属复合薄板的新技术。该技术的主要工艺特点是:以种金属为基材，在其表面覆上另一种金属粉末，通过将两者共同轧制和适当的后处理工艺，形成金属复合板带，板带表面金属轧制覆盖层的厚度可以控制在100一2000um的范围内。

2.轧制镀的工艺过程

(1)表面预复合将选定的基材进行表面活化处理后，通过特殊工艺在其表面沉积一定厚度的金属粉末。

(2)复合轧制将经表面预复合的板带进行复合轧制，其目的是进一步强化覆层与基材的结合，改善复合板带材的表面质量，实现产品规格所需的最终几何尺寸。

(3)扩散处理对轧制后的板材进行扩散处理，确保覆层与基材实现冶金结合。

3.轧制镀的原理

粉末轧制镀与传统双金属带复合轧制相同，金属在轧制力作用下的变形可分为滑动变形和粘结变形，如图1-2所示。在滑动变形区( I区)内，粉末颗粒与轧辊、粉末颗粒与基材、粉末颗粒与颗粒之间均发生相对滑动，这种滑动促使金属粉末颗粒外表面包裹的氧化膜破裂甚至脱落。在轧制力作用下，较大直径的粉末颗粒开始发生延展变形，较小直径的粉末颗粒通过滑动填充到大直径颗粒的间隙中。在金属粉未颗粒尚未压紧变形之前，金属颗粒的变形是均匀向四周延展的。随变形量的增大，粉末颗粒逐渐变扁、展宽，彼此接近，间際越来越小，最后相互焊合连接成一体。进人粘结变形区(I区)，已延展成一体的金属粉末与钢铁基体发生粘结，完成板带表面金属粉末镀层的轧制过程。

用PPR法制备金属复合板带的轧制过程是种不同于单一板材或板材叠轧的工件不对称轧制。在轧制力的作用下，粉末由疏松的颗粒状延展成致密的片状，并与金属基体结合成体，粉末的变形与轧制力的大小有关，并直接影响复合板材的质量，而轧制压力又受粉末材料的特性、覆层厚度、颗粒大小的影响。另外，轧制过程中的摩擦力也对轧制压力有影响。

4.轧制镀层的结合机理

在粉末轧制镀过程中，金属粉未颗粒在延展变形、连接成片的同时还对基材产生挤压作用，致使基材金属表面租化，并与延展成片的粉末颗粒覆层紧密地“冷焊合”在一起完成复合过程，经过后线的扩散退火热处理，使镀层和基体之间达到扩散结合。

5.轧制镀的应用

至今利用粉末轧制缺已成功地开发出铜钢、黄铜钢、铝钢、钛-钢、不锈钢一钢、银钢等表面复合金属板带材，制复合材料已经用于卷帘门等领域的工业生产。

1. Presentation of rolling plating
Powder rolling powder and oling method is called metal powder-strip composite rolling plating, which is abbreviated as PPR method. It is a new technology for preparing bimetal composite sheet developed by Kunming University of Technology in the 1990s. The main technological characteristics of this technology are that one kind of metal is used as the base material, and another kind of metal powder is coated on its surface. By rolling the two together and proper post-treatment process, a metal composite strip is formed. The thickness of the metal rolling coating on the surface of the strip can be controlled in the range of 100-2000um.
2. Process of rolling and plating
(1) Surface pre-compounding will activate the selected substrate and deposit a certain thickness of metal powder on its surface by special process.
(2) Compound rolling is the process of composite rolling of pre-composite strips. Its purpose is to further strengthen the combination of cladding and substrate, improve the surface quality of composite strips, and realize the final geometric size required for product specifications.
(3) Diffusion treatment is applied to the rolled sheet to ensure the metallurgical bonding between the cladding and the base metal.
3. Principle of Rolling Plating
Powder rolling plating is the same as traditional bimetal strip composite rolling. Metal deformation under rolling force can be divided into sliding deformation and bonding deformation, as shown in Figure 1-2. In the sliding deformation zone (zone I), relative sliding occurs between powder particles and rolls, between powder particles and matrix, between powder particles and particles, which causes the oxide film wrapped on the outer surface of metal powder particles to rupture or even fall off. Under the action of rolling force, the larger diameter powder particles begin to deform, and the smaller diameter powder particles are filled into the gap of the larger diameter particles by sliding. The deformation of metal particles extends uniformly to all sides before the metal particles are compacted and deformed. With the increase of deformation, the powder particles become flatter and wider, close to each other, smaller and smaller, and finally weld each other to form a whole. In the bonding deformation zone (zone I), the metal powder which has been extended into a whole bonds with the iron and steel matrix to complete the rolling process of the metal powder coating on the strip surface.
The rolling process of metal clad strip prepared by PPR is an asymmetric rolling process different from that of single sheet or laminated sheet. Under the action of rolling force, the powder extends from loose granular to compact sheet and integrates with metal matrix. The deformation of powder is related to the rolling force and directly affects the quality of composite plate. The rolling pressure is also affected by the characteristics of powder material, the thickness of coating and the size of particles. In addition, the friction force during rolling also affects the rolling pressure.
4. Bonding mechanism of rolled coating
In the process of powder rolling and plating, the ungranulated metal powders exert extrusion effect on the substrate while stretching deformation and joining into sheets, which results in the renting of the metal surface of the substrate, and completes the composite process by "cold welding" closely with the coatings of the powder particles stretching into sheets. After the diffusion annealing heat treatment of the rear line, the diffusion bonding between the coating and the substrate is achieved.
5. Application of Rolling Plating
So far, surface composite metal sheets and strips such as copper steel, brass steel, aluminium steel, titanium-steel, stainless steel and silver steel have been successfully developed by powder rolling. Composite materials have been used in the industrial production of rolling shutters and other fields.

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