ISO-4521-1985.pdf

International Standard ,NTERNAT,ONAL ORGAN,ZAT,ON FOR STANDARDIZATION.MEXYHAPOAHAR OPTAHM3ALblA fl0 CTAHAAPTH3ALMH.ORGANlSATlON INTERNATIONALE DE NORMALISATION Metallic coatings - Electrodeposited silver and silver alloy coatings for engineering purposes RewZtements m b) galling (cold welding) will occur when two similar silver surfaces (for example two “bright” or two “dull” coatings) are used in sliding contact. Attention is also drawn to the expression in certain contexts of silver contents in terms of parts per thousand (by mass), also known as “thousandths” (milliemes) or “fineness“. In this International Standard, percentages by mass to one decimal place are used. 1 Scope and field of application This International Standard specifies requirements for elec- trodeposited coatings of silver and its alloys for electrical, electronic and other engineering applications on metallic and non-metallic materials. Such coatings may or may not be subject to subsequent machining. It does not apply to coatings on screw threads see IS0 4642, Threaded components - Electroplated coatings components (at present at the stage of draft) or to coatings on sheet or strip in the unfabricated form. 2 References IS0 1463, Metallic and oxide coatings - Measurement of coating thickness - Microscopical method. IS0 2964, Metallic and other non-organic coatings - Defi- nitions and conventions concerning the measurement of thickness. IS0 2177, Metallic coatings - Measurement of coating thickness - Coulometric method by anodic dissolution. 1) IS0 4516, Metallic and related coatings - Vickers and Knoop microhardness tests. I SO 4519, Electrodeposited metallic coatings and related finishes - Sampling procedures for inspection by attributes. IS0 4522, Metallic coatings - Test methods for elec- trodeposited silver and silver alloy coatings - Part 7 : Determination of coating thickness. Part 2 : Adhesion tests. Part 3 : Residual salts test. 2) IS0 4599, Metallic coatings - Thioacetamide corrosion test I TAA test). 1) At present at the stage of draft. (Revision of IS0 2177-1972.) 2) At present at the stage of draft. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/26/2007 21:29:26 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 4521-1985 (E) IEC Publication 68-2-20, Basic environmental testing pro- cedures - Test T : Soldering. h) any requirements for anti-tarnish treatment, the type of treatment and methods of test to be applied; j) requirements for solderability and the method of test to be used (see 11.8); 3 Definitions For the purpose of this International Standard, the definitions of IS0 2064, especially the following, apply. k) any requirements for freedom from contamination of the finished product (see 11 .lO). significant surface : The part of the article covered or to be covered by the coating and for which the coating is essential for serviceability and/or appearance. 5 Basis material This International Standard specifies no requirements for the condition, finish or surface roughness of the basis material prior to electroplating. However, it should be recognized that the surface roughness of the coating will be dependent on the initial surface roughness of the basis material and this shall not, therefore, be a cause for rejection of the silver or silver alloy coating. 4 Information to be supplied by the purchaser to the electroplater 4.1 Essential information The following information shall be supplied by the purchaser to the electroplater : a) the number of this International Standard (IS0 4521); 6 Pretreatment b) the classification number of the coating required (see clause 8 and 11.2); 6.1 Mercury compounds shall not be used in the pretreat- ment of basis materials. c) the significant surface of the article to be electroplated indicated, for example, on drawings or by the provision of suitably marked samples; 6.2 To avoid poor adhesion, it is usual to use a silver strike to prevent the chemical deposition of silver and silver alloys on to the basis material. For electroplating certain alloys, a gold strike may be preferable. d) the surface appearance (see 11 .l); e) the method(s) of adhesion testing to be employed (see 11.5); 7 Sampling f) the sampling procedure to be adopted (see clause 7). A random sample of the size required by IS0 4519 shall be selected from the inspection lot. The articles in the sample shall be inspected for conformance to the requirements of this Inter- national Standard and the lot shall be classified as conforming or not conforming to each requirement according to the criteria of the sampling plans in IS0 4519. 4.2 Additional information The following additional information may be required and, if so, shall be specified by the purchaser : a) the minimum silver content of the coating see 8 cl1 and details of any intentional alloying elements (see 11.4); 8 Classification number b) the nature of the basis material, its surface condition and roughness (see clause 5); The classification number comprises : c) any requirements for stress relief before electroplating and/or hydrogen embrittlement relief after electroplating (see clause 9); a) the chemical symbol for the basis metal or for the prin- cipal metal, if an alloy, or in the case of non-metallic materials the letters NM followed by an oblique stroke; d) any special requirements, including the thickness, for undercoats (see clauses 6 and 10); b) if appropriate, the chemical symbol(s) for the undercoat metal(s), as shown by the examples given in table 1, follow- ed by an oblique stroke; e) any requirements for corrosion resistance and/or porosity testing and the methods of test to be used (see 11.3); c) the chemical symbol for silver, Ag, followed if required by a number in parentheses representing the minimum silver content, expressed as a percentage by mass, of the silver coating to one decimal place; f) the electrical properties of the coating and the methods of test to be used (see 11.6); d) a number indicating the minimum thickness, in micrometres, of the silver or silver alloy coating on the significant surface. g) the microhardness of the coating and the test method from IS0 4516 to be used (see 11.7); 2 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/26/2007 21:29:26 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 4521-1985 (E) Table 1 - Symbols Examples of complete classification numbers are - a silver coating, having a thickness of 20 pm (mini- mum), on brass, has the classification number Cu/Ag 20 - a 99,9 % silver coating, having a thickness of 10 pm (minimum), on steel, using a nickel undercoat, has the classification number Fe/Ni/Ag(99,9) 10. 9 Heat treatment of steels 9.1 General Heat treatment as specified in 9.3 and 9.4 shall be performed on certain basis metals to reduce the risk of damage by hydrogen embrittlement. In all cases, the duration of heat treatment shall commence from the time at which the whole of each part attains the specified temperature. Parts made from steels with maximum specified tensile strengths greater than 1 050 MPat) (corresponding hardness values approximately 34 HRC, 340 HV or 325 HB) and surface- hardened parts will require heat treatment. Preparation in- volving cathodic treatments in alkaline or acid solutions shall be avoided. Additionally, the selection of electroplating solutions with high cathodic efficiencies is recommended for steel com- ponents with tensile strengths greater than 1 450 MPa (corresponding hardness values approximately 45 HRC, 440 HV or 415 HB). 9.2 Categorization of steels 9.2.1 With the exception of surface-hardened parts (see 9.3.2 and 9.4.2), the heat-treatment conditions shall be selected on the basis of the specified maximum tensile strength. Steels shall be categorized according to specified maximum tensile strength according to table 2. If the steel specification is only in terms of minimum tensile strength, the corresponding maximum tensile strength shall be determined from table 2. Table 2 - Categories of steels and maximum tensile strengths corresponding to specified minimum tensile strengths Minimum specified Corresponding maximum tensile strength, R,.,i“ tensile strength, R, (MPa) (MPa) R mmin Ooo R mmax ' 050 1000 R,in 1400 1 050 R, 1 450 1400 Rmmin 1750 1450 R, 1800 1750 R,in 1800 Rrnmax 1) 1MPa = lN/mmz 9.2.2 If neither the maximum nor the minimum tensile strength is specified for the steel, Vickers hardness values of 340, 440 and 580 HV shall be regarded as equivalent to maximum tensile strengths 1 050, 1 450 and 1 800 MPa, res- pectively, and these strengths shall be used to select the heat- treatment conditions. 9.3 Stress relief before electroplating 9.3.1 The conditions given in table 3 are recommended if the purchaser requires the parts to be stress relieved before elec- troplating, although different conditions, namely suitable com- binations of shorter periods at appropriate higher temperatures, may be used if they have been shown to be effective. The heat treatment shall be carried out before the commencement of any preparation or cleaning treatment using aqueous solutions. 1 Table 3 - Heat-treatment conditions for stress relief before electroplating (excluding surface-hardened parts) Maximum specified tensile Temperature Time strength, R, MPa OC h R mmax ( ' 050 None required - 1 050 R,max 1 450 190 to 220 1 1450 R, 1800 190 to 220 18 180 Rrnmax 190 to 220 24 J 9.3.2 Surface-hardened parts shall be heat treated at 130 to 150 OC for not less than 5 h or for shorter periods at higher temperatures if the resulting loss of surface hardness of the substrate is acceptable. 9.3.3 If stress relief is given after shot peening or other cold working processes, the temperature shall not exceed 220 OC. 9.4 Hydrogen embrittlement relief after electroplating 9.4.1 The treatment shall be carried out as soon as possible, and in any case not later than 4 h after electroplating, ac- cording to the conditions specified in table 4. Table 4 - Heat-treatment conditions for hydrogen embrittlement relief after electroplating (excluding surface-hardened parts) I Maximum specified tensile Temperature Time strength, R, MPa OC h R mmax ( 1 050 None required - 1 050 Rmmax 1 450 190to 220 8 1 450 R, 1800 190to 220 18 1 800 R, 190 to 220 24 3 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/26/2007 21:29:26 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 4521-1985 (E) 9.4.2 Surface-hardened parts shall be heat treated at a temperature between 190 and 220 C for not less than 2 h. 9.4.3 Other temperatures and durations may be specified and used if they have been shown to be effective for the particular part, and are acceptable to the purchaser. However, parts shall not be heat treated above their tempering temperature. NOTE - Attention is drawn to the fact that the heat treatments specified can cause interdiffusion of the silver coating and the substrate. Undercoats of nickel reduce this effect. However, see also note 3 to clause 10. 10 Requirements for undercoats The thickness requirements for undercoats given in table 5 are minimum values. For arduous conditions of service, greater thicknesses may be required and shall be specified by the pur- chaser see 4.2 d)l. NOTES 1 See 6.2 for guidance on avoidance of poor adhesion. 2 An undercoat of low stress may be essential. 3 For certain applications, undercoats of copper and/or nickel may be undesirable. In such cases, the undercoat may be replaced by at least the same thickness of silver or silver alloy. Table 5 - Requirements for undercoats Basis material Undercoat(s) Minimum thickness of undercoat(s) (urn) Copper Copper alloys, notably free-cutting brass containing lead None - Cu (copper) or Ni (nickel)t) may be required To be agreed Ferrous materials (other than austenitic stainless steel) Ni tnickebt) Cu/Ni (copper + nickel) 10 10 (Cu) + 5 (Ni) Austenitic stainless steel An acid nickel strike Woods bath2)l will normally be required Thin coating, to promote adhesion of the silver coating Zinc and zinc alloys 1 Cu/Ni (copper + nickel) 1 8fCu) + lO(Ni) Aluminium and aluminium alloys Other basis materials and basis metal with soldered joints Ni tnickel)t)3) Nickel) or copper may be required to meet functional or other requirements of this International Standard 20 To be agreed 1) Low stress nickel undercoats should normally be used. 2) A Woods bath consists of a solution of 240 g of nickel chloride hexahydrate (NiCl2.6H20) and 85 ml of 36 % (m/m) hydrochloric acid per litre. The parts are made anodic for not more than 2 min and then cathodic for 6 min, using depolarized nickel electrodes, without anode bags, at room temperature and a current density of 300 A/m2. If current reversal is not feasible, the anodic treatment can be replaced by immersion in the solution, without current flow, for 15 min. 3) An initial copper coating may be employed under the nickel coating but the thickness of the nickel coating should not be reduced If required, the thickness of any undercoat shall be determined by the microscopical method specified in IS0 1463 or the coulometric method specified in IS0 2177. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/26/2007 21:29:26 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 4521-1985 (E) 11 Requirements for silver and silver alloy coatings If the tests given in 11.2, 11.3, 11.5 and 11.7 are to be carried out, this should be done in the absence of any anti-tarnish treatment referred to in clause 12. The tests specified in 11.4 and 11.6 shall be carried out after the final treatment. 11.1 Appearance The electroplated article shall be free from extraneous soil and from damage. Over the significant surface, the electroplated article which is not to be machined subsequently shall be free from electro- plating defects such as pits, roughness, cracks, or uncoated areas visible when viewed at a magnification of X 8 (see the note). In addition, blistering or other signs of poor adhesion cannot be tolerated on any surface of the article. Silver and silver alloy electroplated articles which are to be machined subsequently shall be free from excessive nodulation and treeing at the edges and from imperfections detrimental to subsequent fabrication. On articles where a c