The science of scratch resistance in electroplating
1. The hardness of the plating material
2. Plating layer thickness
3. Microscopic structure of plating layer
4. Adhesion of the plating layer to the substrate
5. Internal stresses of plating layer
Types of plating and their properties in resistance to scratches
1. Nickel Plating
- Semi-bright nickel: Usually harder and more wear resistant than bright nickel. This type of plating is great for increasing scratch resistance, especially when surface appearance is less of a priority.
- Bright Nickel: Contains additives to create a shiny surface that may be a little softer. However, by adjusting the process parameters, the hardness and scratch resistance can also be improved in bright nickel.
2. Chrome Plating
- Hard chrome: It is usually plated thicker than decorative chrome and can range in thickness from 10 microns to over 100 microns. This type of plating is ideal for parts that are subject to heavy wear, such as engine parts, cutting tools, and dies. Plating thickness Hard chrome is directly related to increased scratch and wear resistance.
3. Copper Plating
4. Zinc Plating
5. Alloy Plating
- Nickel-phosphorus: Depending on the amount of phosphorus, it can have different properties. High-Phosphorus Nickel-Phosphorus has good corrosion resistance, while Mid-Phosphorus Nickel-Phosphorus is harder and offers better wear and scratch resistance.
- Nickel-Boron: This alloy is very hard and provides excellent wear and corrosion resistance, making it suitable for tough applications. Micron plating of these alloys helps to control the composition and structure of the layer and ensures the desired properties.
Optimum plating thickness for scratch resistance
Light Duty Applications
- Nickel: 5 to 20 microns. For these applications, a semi-bright or bright nickel layer of this thickness can provide adequate resistance to everyday scratches.
- Chrome (decorative): 1 to 10 microns. Decorative chrome is mainly used for appearance, but this thin layer can also slightly increase scratch resistance.
Medium Duty Applications
- Nickel: 20 to 50 microns. The use of semi-bright nickel with this thickness, along with a thin layer of chrome, provides significant scratch resistance.
- Hard chrome: 10 to 30 microns. For parts that need more resistance to wear, but the high thickness of hard chrome may be problematic.
Heavy Duty Applications
- Hard chrome: 30 to 100 microns or more. In these applications, a high thickness of hard chrome is necessary to ensure resistance to scratches and wear during the useful life of the part.
- Nickel-Phosphorus (High-Phosphorus or Mid-Phosphorus): 20 to 100 microns. These alloys, especially when applied by the micron plating process, exhibit excellent wear and scratch resistance and are used as a substitute for hard chromium in some applications.
- Nickel-boron: 10 to 50 microns. The extreme hardness of this alloy makes it ideal for parts that require maximum wear resistance.
Specialized Applications
Surface preparation process
- Cleaning: Removing grease, oil, dust, and other contaminants from the surface of the piece. This step can include alkaline, acidic, and ultrasonic washing. Pickling: Removal of rust, oxides, and surface scales of the metal. Activation: Often performed in the final step before plating to ensure that the base metal surface is ready to accept the plating layer and to prevent the formation of unwanted oxides.
Quality control in electroplating
Controlling the thickness of the plating layer
- Measurement methods: Measurement of plating layer thickness using equipped devices such as magnetic micrometers (for ferromagnetic metals), eddy current micrometers, and metallographic methods (microscopic cutting). Plating thickness must be in accordance with the specified specifications at all points of the surface.
Hardness measurement
- Hardness tests: Perform hardness tests on the plating layer (such as Rockwell, Vickers, or Micro Vickers tests) to ensure the required hardness is achieved. This test is directly related to scratch resistance.
Adhesion test
- Bending Test: Bending the plated piece to check for cracks or detachment of the plating layer.
- Scratch Test: Applying a specific force with a sharp tip to evaluate the resistance to scratching.
- Heat Treatment Test: Placing the piece at high temperatures to check adhesion stability.
Visual inspection
Functional tests
Micron plating: accurate and specialized
- Exceptional uniformity: Micron plating makes it possible to achieve layers of very uniform thickness, even on surfaces with complex geometry. This uniformity prevents the creation of local weak points that are prone to scratching. Structure control: In micron plating processes, it is possible to precisely control the grain structure, porosity, and internal stresses of the layer. This control directly affects the hardness and scratch resistance.
- Reduction of material consumption: By carefully controlling the thickness, excessive consumption of plating materials is avoided, which, in addition to economic savings, leads to the creation of more optimal layers in terms of mechanical properties.
- Compliance with precise tolerances: In industries where tolerances Dimensions are very strict (such as electronics and precision instruments), micron plating is the only possible solution.
