ASTM A153 governs zinc coatings applied by the hot-dip process to hardware products such as castings, fasteners, rolled, pressed, and forged products, and miscellaneous threaded objects that will be centrifuged, spun, or otherwise handled to remove excess zinc. The hot-dip galvanizing process for articles galvanized to ASTM A153 is identical to the process required under ASTM A123 with the exception the iron and steel hardware in ASTM A153 are centrifuged or spun to remove excess zinc.
ASTM A153/A153M Requirements
- Coating Thickness/Weight depends on the material category and steel thickness, values are listed in Table 3
- Threaded Products areas with threads are not subject to the coating thickness requirement
- Finish continuous, smooth, uniform
- Embrittlement high tensile strength fasteners (>150ksi) and castings can be subject to embrittlement
- Appearance free from uncoated areas, blisters, flux deposits and gross dross inclusions as well as having no heavy zinc deposits that interfere with intended use
- Adherence the entire coating should have a strong adherence throughout the service life of hot-dip galvanized steel
There are fabrication steps that may impair the corrosion protection of the hot-dip galvanized coating; however, flaking or damage to the coating because of this is not case for rejection. In all cases, good steel selection results in the formation of a higher quality coating and finish on the product. The corrosion protection coating for threaded products is applied after the product has been fabricated and further fabrication may compromise the corrosion protection system. The one exception to this rule is the internal threads of a nut that should be over-tapped after the coating is applied in order to accommodate the coating thickness change on the thread of the bolts. In this case, the zinc on the bolt threads provides the corrosion protection to the uncoated threads in the nut.
There are certain fabrication techniques that can induce stresses into the steel and lead to brittle failure. There are precautions given in ASTM A143/A143M that should be taken in order to prevent embrittlement. In addition, selecting steels with appropriate chemistries can help prevent embrittlement of malleable castings. A reproduction and summary of the table given in ASTM A153/A153M, (Table 3), gives the different classes of products and the minimum coating thickness required by the specification.
|Thickness or Weight (Mass) of Zinc Coating for Various Classes of Material|
|Weight (Mass) of Zinc Coating, oz/ft2 (g/m2) of Surface, minimum||Coating Thickness, mils (microns), Minimum|
|Class of Material||Average of Specimens Tested||Any Individual Specimen||verage of Specimens Tested||Any Individual Specimen|
|Class A - Castings - Malleable Iron, Steel Class B - Rolled, Pressed, and Forged articles (except those which would be included under Classes C and D)||2.00 (610)||1.80 (550)||3.4 (86)||3.1 (79)|
|B-1 - 3/16 in. (4.76 mm) and over in thickness and over 15in. (381 mm) in length||2.00 (610)||1.80 (550)||3.5 (85)||3.1 (79)|
|B-2 under 3/16in. (4.76mm) in thickness and over 15in. (381mm) in length||1.5 (458)||1.25 (381)||2.6 (66)||2.1 (53)|
|B-3 any thickness and 15in. (381mm) and under in length||1.30 (397)||1.10 (336)||2.2 (56)||1.9 (48)|
|Class C - Fasteners over 3/8in. (9.52mm) in diameter and similar articles. Washers 3.16in. and 1/4in (4.76 and 6.35 mm) in thickness||1.25 (381)||1.00 (305)||2.1 (53)||1.7 (43)|
|Class D - Fastners 3/8in (9.52mm) and under in diameter, rivets, nials and similar articles. Washers under 3/16in (4.76mm) in thickness||1.00 (305)||0.85 (259)||1.7 (43)||1.4 (36)|
|Note 1: Length of the piece, stated in Classes B-1, B-2, B-3, refers to the finished dimensiosn of the piece after fabrication|
© 2021 American Galvanizers Association. The material provided herein has been developed to provide accurate and authoritative information about after-fabrication hot-dip galvanized steel. This material provides general information only and is not intended as a substitute for competent professional examination and verification as to suitability and applicability. The information provided herein is not intended as a representation or warranty on the part of the AGA. Anyone making use of this information assumes all liability arising from such use.