Metal plating is a long-established process. These days only plating techniques using a liquid tend to be referred to as ‘plating’. Metallizing refers to the process of coating metal on non-metallic objects.
Gold plating deposits a thin layer of gold on the surface of other metal, usually copper or silver, and is often used in electronics to provide a corrosion-resistant electrically conductive layer on copper (e.g. electrical connectors and printed circuit boards).
Because copper tends to diffuse through the gold layer causing tarnishing and oxide / sulphide formation, a barrier metal – usually nickel – tends to be sandwiched in between the two metals.
Gold plating for ornamental purposes is usually referred to as gilding.
Silver plating is often used as a cheaper replacement for gold in the electronics industry. However the underlying copper can corrode and flake off the silver plating in environments of high humidity.
Rhodium plating is occasionally used on white gold, silver or copper and its alloys, with a nickel barrier layer to prevent contamination of the rhodium bath with the silver and copper.
Chrome plating is a finishing treatment utilizing the electrolytic deposition of chromium.
Bright chrome: the most common use of chrome plating, achieving a corrosion-resistant mirror-like finish for metal furniture frames and automotive trim. Bright chrome typically comprises a 10-µm layer over an underlying nickel plate.
Hard chrome: a thicker deposit (up to 1000 µm) traditionally used in industrial equipment to reduce friction and wear.
Zinc plating – galvanization
Zinc coatings form a barrier to prevent the protected metal from oxidizing and by acting as a sacrificial anode if this barrier is damaged. Zinc oxide is a fine white dust that doesn’t cause the substrate's surface integrity to break down as it is formed (unlike iron oxide). Zinc oxide can also act as a barrier to further oxidation (similar to the way aluminium and stainless steels are protected by their oxide layers).
Tin-plating is used extensively to protect both ferrous and nonferrous surfaces. Tin’s non-toxic, ductile and corrosion resistant properties make it an ideal metal for the food processing industry.
Tin’s excellent ductility allows a tin coated base metal sheet to be formed into a variety of shapes without damaging the surface tin layer. It provides sacrificial protection for copper, nickel and other non-ferrous metals (but not steel).
Because tin protects the base metal from oxidation (thus preserving its solderability), tin is also widely used in the electronics industry. Sometimes lead is added to prevent the growth of metallic ‘whiskers’ in compression stressed deposits, thus avoiding electrical shorting.
Alloy plating is used where two or more metals need to be co-deposited resulting in an electroplated alloy deposit. Nickel-Cobalt is a common electroplated alloy.
Depending on the alloy system, an electroplated alloy may be solid solution strengthened or precipitation hardened by heat treatment to improve the plating's physical and chemical properties.
Metal matrix composite plating is manufactured when a substrate is plated in a bath containing a suspension of ceramic particles. The size and composition of these particles can be carefully selected to fine-tune the deposit for wear resistance, high temperature performance, or mechanical strength.
Tungsten carbide, silicon carbide, chromium carbide, and aluminium Oxide (alumina) are commonly used in composite electroplating.
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