The specification ASTM A153/A153M applies 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 requirements for ASTM A153/A153M are very similar to
those stated earlier for ASTM A123/A123M, except for the addition of threaded
products and embrittlement requirements.
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
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