¿Cuántas de las diez pruebas de rendimiento más importantes para el electrochapado conoces?

Electroplating is a method where a workpiece is immersed in a solution containing metal ions to be deposited, and upon application of an electric current, a thin metallic film is precipitated onto the surface of the workpiece. Electroplating can impart excellent appearance, good corrosion resistance, and wear resistance to various metal and non-metal components. It also enables the surface of components to acquire various special functions, transforming them into new functional materials, and can even serve as a means to form certain metal-matrix composite materials. Therefore, electroplating finds widespread application across various industrial sectors. So, how is the performance of electroplating evaluated? Below, we will interpret the top ten performance tests for electroplating.

Appearance inspection of the electroplated layer on metal components is the most fundamental and commonly used test. Workpieces with unacceptable appearances do not require testing for other items. During inspection, visual observation is used to classify workpieces into three categories: acceptable, defective, and scrap. Appearance defects include pinholes, pits, nodules, peeling, blistering, detachment, uneven surfaces, spots, burning, shadows, dendritic and spongy deposits, as well as areas that should have been plated but were not.

Surface roughness measurement falls under microscopic length measurement, with methods such as the comparison method, optical method, and stylus method currently employed. The contour method within the stylus method is widely used due to its advantages of small size, light weight, high magnification, and fast measurement speed.

Coating brightness is an indicator measured for plated components with high decorative requirements. Brightness refers to the ratio and intensity of light reflected from the coating surface under the action of incident light at a certain illuminance and angle. Visual inspection and sample comparison methods are typically used to evaluate the brightness of plated components. For planar plated components, a photometer can yield good results.

Coating adhesion strength, also known as coating bonding strength, refers to the quality of the bond between the coating and the substrate or intermediate coating. The adhesion strength of the coating has a direct impact on decorative performance and protective effects, making it an important quality inspection indicator for metal coatings.

Selection of Test Methods for Metal Coating Adhesion Strength

The thickness and uniformity of an electroplated layer are important indicators of coating quality, significantly affecting product reliability and service life. Thickness measurement methods for electroplated layers are divided into two categories: destructive and non-destructive. Destructive measurement methods include the chronometric liquid flow method, drop thickness measurement method, coulometric method, and metallographic method, among others. Non-destructive measurement methods include the magnetic method, eddy current method, beta-ray backscattering method, and X-ray spectroscopy method, among others.

Thickness Testing Methods and Corresponding Standards

Porosity in a coating refers to fine channels or pores extending from the coating surface to the base metal, affecting the coating's protective ability. Methods for measuring porosity include the filter paper patch method, immersion method, electrocoating method, and gas permeation method, among others.

Coating Porosity Testing Methods

Hardness is an important mechanical property of coatings. The hardness of a coating depends on the crystalline structure of the deposited metal. To eliminate the influence of the substrate material and limitations on indentation size due to coating thickness, the microhardness method is generally used.

Vickers/Knoop Hardness Testers

Vickers Hardness Indentation (Left) and Knoop Hardness Indentation (Right)

Internal stress in a coating refers to a balanced stress within the coating without external loads. This stress is caused by factors affecting deposition during the electroplating process, leading to metal lattice defects. Certain metal ions, anions, and organic additives in the plating solution can significantly increase the internal stress of the coating. Internal stress in the coating can lead to phenomena such as blistering, cracking, and peeling during storage and use, as well as stress corrosion and reduced fatigue strength under external forces. Methods for measuring internal stress in coatings include the bent cathode method, rigid flat strip method, and spiral contractometer method, among others. Test methods can refer to ASTM B636.

Typical Hydrogen Embrittlement Fracture

Coating brittleness is an important indicator of the coating's physical properties. Brittleness often leads to coating cracking, reduced bonding strength, and even direct impact on its use value. Coating brittleness testing generally involves deforming the sample under external force until the coating cracks, and then using the degree of deformation or deflection value at which the coating cracks as a basis for evaluating coating brittleness. Testing can refer to standard ASTM F519.

Coating ductility refers to the ability of the coating to resist fracture or cracking when subjected to plastic or elastic deformation, or both simultaneously, under external force. Methods for measuring coating brittleness include delayed fracture testing, slow bending testing, and stress ring testing, among others. Methods for measuring coating toughness include tensile testing and bending testing, with reference standards such as GB/T 15821, ASTM B489, and ASTM B490.

Coating solderability refers to the ease with which solder flows on the surface of the metal to be soldered, i.e., the ability of the coating surface to be wetted by molten solder. Different coatings have varying abilities to be wetted by the same molten solder; even the same coating may have different solderability due to differences in impurity content and coating structure. Therefore, testing the solderability of coatings can better understand the matching between the coating and solder, enabling targeted selection of solder to meet the solderability requirements of electronic processes. Solderability testing methods mainly include slot soldering, ball soldering, and wetting weighing methods, with reference standards such as GB/T 16745 and ASTM B678.

Salt Spray Test Chamber

Corrosion resistance refers to the ability of an electroplated product to resist environmental erosion, making it an important performance indicator of the coating. Whether for protective, decorative, or functional coatings, there are strict requirements for the corrosion resistance of the coating under certain environmental conditions. Once the coating is corroded, the product cannot perform its intended function. Corrosion resistance testing is an important means to evaluate coating performance and product service life, playing a significant role in ensuring the safe use of products.

Coating Corrosion Resistance Testing Methods

Abrasion Tester

Some coatings are used in areas subject to friction and require good wear resistance. Generally, it is believed that a coating with high hardness has correspondingly good wear resistance. Therefore, sometimes people compare the hardness of coatings to assess their wear resistance. However, this method is not very scientific because the wear resistance of a coating depends not only on hardness but also on factors such as the material and surface of the object in contact, the load during friction, lubrication conditions, and temperature. Therefore, wear resistance testing of coatings mostly involves simulating actual usage conditions and conducting abrasion tests. The test equipment is an abrasion tester, with reference standards such as GB/T 12967 and ASTM F1978.