Surface treatment is a process to artificially form a surface layer on the surface of the matrix material that is different from the mechanical, physical and chemical properties of the matrix. The purpose of surface treatment is to meet the requirements of corrosion resistance, wear resistance, decoration or other special functions of products. For metal castings, we usually use surface treatment methods such as mechanical grinding, chemical treatment, surface heat treatment and spraying.
Surface deformation strengthening refers to the surface strengthening process that causes plastic deformation of steel parts at room temperature to form surface compressive stress, so as to improve its surface hardness and generate favorable residual compressive stress distribution. The process is simple and the cost is low. It is an important process measure to improve the fatigue resistance and prolong the service life of steel parts.
Shot peening strengthening is a technology to spray a large number of high-speed moving projectiles onto the surface of the part, just like countless small hammers hitting the metal surface, so that the surface and subsurface of the part will have certain plastic deformation to achieve strengthening.
Application: For parts with complex shape, it is carried out after grinding, electroplating and other processes.
The free rotating quenched steel roller is used to roll the machined surface of the steel piece to produce plastic deformation, flatten the rough peaks on the surface of the steel piece, and form favorable residual compressive stress, so as to improve the wear resistance and fatigue resistance of the workpiece.
Surface finishing refers to extruding steel balls or other shapes of finishing tools with a diameter slightly larger than the hole diameter through the machined inner hole of the workpiece at room temperature to obtain an accurate, smooth and strengthened surface.
Surface quenching refers to the heat treatment method of strengthening the surface of parts after austenitizing the surface layer with rapid heating without changing the chemical composition and central structure of steel.
The method of rapidly heating the workpiece surface by using alternating current to induce huge eddy current on the workpiece surface.
The method of directly heating the workpiece surface with acetylene flame. The cost is low, but the quality is not easy to control.
The method of heating the workpiece surface with high energy density laser. High efficiency and good quality.
Laser surface strengthening can be divided into laser transformation strengthening treatment, laser surface alloying treatment and laser cladding treatment.
Bluing: The process of heating steel or steel parts to an appropriate temperature in air water vapor or chemicals to form a blue or black oxide film on their surface. Also called blackening.
Phosphating: the process of workpiece (steel or aluminum or zinc parts) immersed in phosphating solution (some acid phosphate based solutions) to deposit a layer of water-insoluble crystalline phosphate conversion film on the surface, which is called phosphating.
Chemical heat treatment is a heat treatment process in which the workpiece is placed in a specific medium for heating and insulation, so that the active atoms in the medium penetrate into the surface of the workpiece to change the chemical composition and structure of the surface of the workpiece, thereby changing its performance.
Chemical heat treatment is also one of the methods to obtain surface hardness and inner toughness. Compared with surface quenching, chemical heat treatment not only changes the surface structure of steel, but also changes its chemical composition. According to the different elements infiltrated, chemical heat treatment can be divided into carburizing, nitriding, multi-element penetration, penetration of other elements, etc. The chemical heat treatment process includes three basic processes: decomposition, absorption and diffusion.
Surface coating strengthening refers to the surface strengthening process of coating one or more layers of other metals or nonmetals on the metal surface by physical or chemical methods.
Objective: To improve the wear resistance, corrosion resistance, heat resistance or surface decoration of steel parts.
Polishing is a finishing method to modify the surface of parts. Generally, only smooth surfaces can be obtained, and the original machining accuracy cannot be improved or even maintained. With different pre machining conditions, the Ra value after polishing can reach 1.6~0.008mm.
It includes wheel polishing, roller polishing and vibration polishing.
Electrochemical polishing is similar to chemical polishing, but the difference is that DC is also used to connect the workpiece to the anode to generate anodic dissolution. It is also polished by taking advantage of the phenomenon that the convex part of the metal surface dissolves faster than the concave part.
Common coating processes include: brush coating, automatic dip coating, manual spraying (including high-pressure airless spraying), spray coating, curtain coating, fluidized bed coating, roller coating, electrostatic spraying, etc.