This standard covers the requirements for hot dip aluminum coating to a sheet steel substrate utilizing a continuous hot dip process. The substrate may be cold or hot rolled sheet steel. Additional requirements or agreements shall be specified by the local business units.

Material Description. The type of coating and its mass and finish are specified by the suffixes added to the basic steel substrate specification number. The first two letters, AL, will designate a continuous hot dip Aluminum coating. The Coating Type is identified by a letter-number combination. T1M is a Type 1 aluminumsilicon alloy. T2M is Type 2 commercially pure aluminum. The coating mass for each side is designated by a minimum value in g/m2. The coating designations for steels supplied under this standard shall reflect coatings weights in metric units. The "M" suffix was added to T1 and T2 for clarification.

Typical Applications. Aluminum coated sheet metal parts consisting of steel substrates described by GMW2, GMW3032 or GMW3399 that are aluminum coated as described herein. Type 1 Coatings are generally specified for heat shields and fuel tanks.

Remarks. This specification supersedes GM6178M for new applications. A conversion from GM6178M to GMW16066 is listed in Appendix A1, Table A1.