Surface Finishing Tutorial

#313 Grades and Symbols of Nickel and Chrome Plating on Aluminum Alloy Substrates

Category : Electroplating

October13, 2017

This standard defines the types of nickel and chrome plating applied on aluminum and aluminum alloy substrates for decorative and anti-corrosion purposes, as well as the plating thickness of the significant surfaces and the corrosion-resistance properties.(The corrosion resistance properties are described in another section.)

[Table] Nickel and chrome plating on aluminum alloy substrates

Grade	Base-coat plating	Base-coat plating Minimum thickness (µm)	Top-coat plating	Top-coat plating Minimum thickness (µm)	Symbol
Grade 1	Nib	10	Cr r	0.1	EP-Al/Ni 10 b, Cr 0.1 r or EP-Al/Nib, Cr r [1]
Grade 2	Nib	20	Cr r	0.1	EP-Al/Ni 20 b, Cr 0.1 r or EP-Al/Nib, Cr r [2]
Grade 3	Nid	30	Cr r	0.1	EP-Al/Ni 30 d, Cr 0.1 r or EP-Al/Nid, Cr r [3]
	Nid	25	Cr mc	0.1	EP-Al/Ni 25 d, Cr 0.1 mc or EP-Al/Nib, Cr mc [3]
	Nid	25	Cr mp	0.1	EP-Al/Ni 25 d, Cr 0.1 mp or EP-Al/Nib, Cr mp [3]
Grade 4	Nid	50	Cr r	0.1	EP-Al/Ni 50 d, Cr 0.1 r or EP-Al/Nid, Cr r [4]
	Nid	35	Cr mc	0.1	EP-Al/Ni 35 d, Cr 0.1 mc or EP-Al/Nid, Cr mc [4]
	Nid	35	Cr mp	0.1	EP-Al/Ni 35 d, Cr 0.1 mp or EP-Al/Nid, Cr mp [4]

What is duplex nickel plating?

This is a type of plating with improved corrosion resistance. Semi-bright or matte nickel plating without containing sulfur is applied as the first layer over a substrate. On the second layer, bright nickel containing approximately 0.05% sulfur is applied over it. Ultimately, chrome plating is deposited over the second layer.
When this plating is exposed in the corrosive environment, the second layer starts dissolving since the second layer is less electrochemically noble than the first layer. The corrosion spreads horizontally over the bright nickel plating applied as the second layer, which prevents the corrosion from being progressed over the first layer. In general, the first layer should be twice as thick as the second layer.

To enhance the anti-corrosive properties, the third plating (trinickel) may be applied. In this case, semi-bright nickel without containing sulfur is applied as the first layer; Trinickel containing the high content of sulfur (0.1 to 0.2%) is applied as the second layer; Bright nickel plating containing approximately 0.05% sulfur is applied as the third layer. This type of plating is adopted in the automotive industry. However, it is not defined by JIS.

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