ASTM B252.pdf
需积分: 4 4 浏览量
2023-02-24
12:28:43
上传
评论
收藏 42KB PDF 举报
Designation: B 252 – 92 (Reapproved 2004)
Endorsed by American
Electroplaters’ Society
Endorsed by National
Association of Metal Finishers
Standard Guide for
Preparation of Zinc Alloy Die Castings for Electroplating
and Conversion Coatings
1
This standard is issued under the fixed designation B 252; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This guide is intended as an aid in establishing and
maintaining a procedure for preparing zinc alloy die castings
for electroplating and conversion coatings. It is primarily
intended for the preparation of Alloys UNS Z33521 (AG-40A)
and UNS Z35530 (AC-41A) (Specification B 86) for electro-
plating with copper, nickel, and chromium (Specification
B 456).
1.2 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
2
B 6 Specification for Zinc
B 86 Specification for Zinc and Zinc-Aluminum (ZA)Alloy
Foundry and Die Castings
B 456 Specification for Electrodeposited Coatings of Cop-
per Plus Nickel Plus Chromium and Nickel Plus Chro-
mium
2.2 Military Standard:
MIL-S-13165C Shot Peening of Metal Parts
3
3. Summary of Practice
3.1 The normal sequence of preparation steps is as follows:
(1) smoothing of parting lines; (2) smoothing of rough or
defective surfaces, if necessary; (3) buffing, if necessary; (4)
precleaning and rinsing; (5) alkaline electrocleaning and rins-
ing; (6) acid dipping and rinsing; and (7) copper striking.
4. Significance and Use
4.1 The performance and quality of electroplated or
conversion-coated zinc alloy die casting depends upon the
surface cleanliness and condition. Various metals are electro-
plated or conversion coatings are established on zinc alloys for
decorative or engineering finish. The common electroplates
applied are usually copper, nickel, and chromium for decora-
tive and functional uses. The common conversion coatings
applied are phosphates, chromates, and anodized coatings.
Electroplated zinc die castings and conversion coatings on zinc
die castings are used in many industries such as the marine,
automotive, plumbing fixtures, and appliance industries.
5. Composition and Characteristics of Zinc Alloy Die
Castings
5.1 The alloys used in the manufacture of zinc alloy die
castings are made with special high-grade zinc conforming to
Specification B 6, alloyed with about 4 % of aluminum, 0.04 %
of magnesium, and either 0.25 (max) or 1.0 % copper (Alloys
UNS Z33521 and UNS Z35530). Impurities such as lead,
cadmium, tin, and iron are held at or below the specified low
levels in Specification B 86.
5.2 Die castings made of Alloys UNS 233521 and UNS
235530 are usually dense and fine grained but do not always
have smooth surfaces. Defects sometimes encountered in the
surface layers include cracks, crevices (cold shut), skin blisters,
and hemispherical pores. Burrs are usually left at parting lines
where fins and gates are removed by die trimming.
5.3 Cast surfaces are frequently contaminated with parting
compounds applied at frequent intervals to die surfaces to
facilitate the ejection of the castings and with water-soluble
oils added to quenching tanks for corrosion inhibition.
5.4 Zinc alloy die castings are chemically active and are
dissolved or etched during prolonged contact with concentrated
solutions of many mineral or organic acids or strongly alkaline
solutions with a pH greater than 10. Immersion periods in such
solutions should be of short duration to avoid roughening.
1
This guide is under the jurisdiction of ASTM Committee B08 on Metallic and
Inorganic Coatings and is the direct responsibility of Subcommittee B08.02 on Pre
Treatment.
Current edition approved April 1, 2004. Published May 2004. Originally
approved in 1951. Last previous edition approved in 1998 as B 252 – 92 (1998).
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
3
Available from Standardization Documents Order Desk, Bldg. 4 Section D, 700
Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS.
1
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
Copyright ASTM International
Reproduced by IHS under license with ASTM
Not for Resale
No reproduction or networking permitted without license from IHS
--````,,-`-`,,`,,`,`,,`---
资源评论
