Coating of carbon steel ISO: 4042 Standard Platings/ Surface Coatings

STANDARD PLATINGS: SURFACE COATINGS
ISO : 4042 (EN ISO 4042) Electroplated coatings
DIN : 267 Part 9

Electroplated coatings/Rivestimenti elettrolitici/Revêtement électrolytiques/ Revestimientos electrolìticos/Elektrolytische Überzüge Code system/Sistema di codifica/Systême de codification/sistema de codificaciòn/Kodifizierungssystem 1. Scope and field of application These technical conditions are in particular related to threaded fasteners (mainly bolts and nuts), but are also applicable to the whole range of mechanical fasteners. 2. Electroplated coatings An electrolytically applied coating shall be defined as a protective metallic layer being deposited onto the surface of metal articles by immersing these parts in an aqueous solution through which an electrical current is passed. Note: The use of the nomenclature “galvanizing” for this treatment is not correct. This information on electroplated coatings corresponds with DIN 267 Part 9 and ISO 4042. 3. Code system The electroplated coatings of mechanical fasteners are designated by a code consisting of a combination of two capital letters and a number. This callout system is built up as follows: – a capital letter for the coating metal (Table 1) – a number for the minimum layer thickness (coating structure) (Table 2) – a capital letter for the degree of gloss and after-treatment (Table 3)

	Table 1. Coating metal				Table 2. Minimum layer thickness (coating structure)
	Code					Layer thickness (coating structure) in µm
	letter	Coating metal	Symbol		Code number	1 coating metal	2 coating metals
	A	Zinc	Zn		0 1)	–	–
	B	Cadmium	Cd		1	3	–
	C	Copper	Cu		2	5	2+ 3
	D	Brass	CuZn		3	8	3+ 5
	E	Nickel	Ni		4	12	4+ 8
	F	Nickel-chrome 1)	NiCr		5	15	5+10
	G	Copper-nickel	CuNi		6	20	8+12
	H	Copper-nickel-chrome1)	CuNiCr		7 2)	25	10+15
	J	Tin	Sn		8 2)	32	12+18
	K	Copper-tin	CuSn		9 2)	40	16+24 3)
	L	Silver	Ag		1) Code number 0 applies to screw threads below
	N	Copper-silver	CuAg		M 1.6, where no specific layer thickness can be specified.
	P	Zinc-Nickel 3)	ZnNi		2) Does not apply to threaded components.
	Q	Zinc-Cobalt 3)	ZnCo		3) Not in ISO 4042
	R	Zinc-iron 3)	ZnFe
	1) Thickness of chrome layer 0,3 µm
	3) Not in ISO 4042

	Table 3. Degree of gloss and after-treatment
	Codeletter	Degree of gloss	Chromating in accordance with DIN 50 941 Process group	Self-color of chromate layer passivation by chromate
	A	mt (dull) (mat)	none 1)	none
	B	mt (dull) (mat)	B	bluish to bluish iridescent 2)
	C	mt (dull) (mat)	C	yellowish glistening to yellowish-brown,iridescent
	D	mt (dull) (mat)	D	olive green to olive brown
	E	bk (bright)	none 1)	none
	F	bk (bright)	B	bluish to bluish iridescent 2)
	G	bk (bright)	C	yellowish glistening to yellowish-brown,iridescent
	H	bk (bright)	D	olive green to olive brown
	J	gl (glossy)	none 1)	none
	K	gl (glossy)	B	bluish to bluish iridescent 2)
	L	gl (glossy)	C	yellowish glistening to yellowish-brown,iridescent
	M	gl (glossy)	D	olive green to olive brown
	N	hgl (high gloss)	none	–
	P	bel (optional)	B, C or D 3) at manufacturer's discretion	as for process group B, C or D
	R	mt (dull) (mat)	F	brownish black to black
	S	bk (bright)	F	brownish black to black
	T	gl (glossy)	F	brownish black to black
	U	all finishes		no chromate treatment
	1) In the case of Zn and Cd		3) Process groups B, C or D in accordance with DIN 50 941 only apply to
	however, process group A		cadmium and zinc coatings. In the case of other electroplated coatings, "P"
	2) Only applies to Zn coatings		in the code symbol signifies "degree of gloss optional".

	Ordering code for electroplated coatings for commercial fasteners
								Copper
		Coating		Zinc-chromated			Nickel	nickel
		Degree of gloss	Glossy	Glossy	Glossy	Glossy	Glossy	Glossy
	Nominal size	Nominal size	Color	Color	Color	Color
	metric	inch	none	bluish	yellowish	black	–	–
	< 5 mm	< 3/16 "	A1J	A1K	A1L	A1T	E1J	G2J
	5 < 10 mm	3/16" < 3/8 "	A2J	A2K	A2L	A2T	E2J	G2J
	> 10 mm	> 3/8 "	A3J	A3K	A3L	A3T	E3J	G3J

Example of coding: A3L means zinc-plating (A in Table 1) with a minimum layer thickness of 8 µm (3 in Table 2) and yellow-chromated with a glossy degree of gloss (L in Table 3). Callout Example: Hexagon bolt DIN 931 - M12 x 50 - 8.8 - A3L. Chromate (passivate) effected immediately after electroplating by short immersing in chromic acid solutions. The chromating process increases the corrosion protection and prevents a starting and a discolouring of the zinc layer. The protective effect of the chromate layer is different depending upon group of procedures (see table).

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