Purchase order shall specify not less than the following:
- Plating thickness (see 3.4.1)
- Basis metal to be plated
- Tensile strength or hardness of the basis metal
- Pre-plate stress relief to be performed by plating processor (time and temperature) if different from 3.1.2
- Special features, geometry or processing present on parts that requires special attention by the plating processor
- Hydrogen embrittlement relief to be performed by plating processor (parameters or reference document) if different from 3.3.1
- Minimum thickness on internal surfaces, if required (see 220.127.116.11)
- Solderability testing, if required (see 3.4.5)
- Quantity of pieces to be plated
Type I – Engineering Plating, 0.0005 to 0.0007 inch (13 to 18 micrometers), tolerance of +0.0002 inch (+5 micrometers)
Type II – (standard) Plating for masking, nominally 0.002 inch (51 micrometers)
(copper flash) – thickness of copper shall be .0001 inch (2.5 micrometers) minimum
Type 1 shall be supplied if no class is specified.
Stress Relief Treatment
All steel parts having a hardness of 40 HRC and above and that are machined, ground, cold formed, or cold straightened after heat treatment shall be cleaned to remove surface contamination and thermally stress relieved before plating. Unless otherwise specified, the following treatment temperatures and times shall be used:
For parts, excluding nitrided parts, having a hardness of 55 HRC and above, and for carburized and induction hardened parts, stress relieve at 275 °F ± 25 °F (135 °C ± 14 °C) for 5 to 10 hours.
For parts having a hardness less than 55 HRC, and for nitrided parts, stress relieve at 375 °F ± 25 °F (191 °C ± 14 °C) for a minimum of 4 hours. Higher temperatures shall be used only when specified or approved by the cognizant engineering organization.
For Peened Parts
If stress relief temperatures above 375 °F (191 °C) are elected, the stress relieve shall be performed prior to peening or AOTCO shall be consulted and must approve the stress relief temperature.
For steel parts 40 HRC and over, contact time with surface activation acids such as hydrochloric, hydrofluoric, and sulfuric acids shall be minimized so as not to produce hydrogen embrittlement (see 8.5).
Aluminum alloys shall be zincate or stannate treated in accordance with ASTM B253 or other method acceptable to AOTCO prior to plating.