Lead-free machinable metal alloys

There aren’t many rules around the lead content of metals for general-purpose machining and the alloy numbers are often misleading, as they only put a limit on the maximum amount of a certain element. I did some research to find alloys that wouldn’t throw up lead-containing dust when worked on a CNC mill.

• 955 bronze is lead-free and often conforms to California’s AB 1953 standard.

• 5052 aluminum is meant for welding and usually doesn’t contain lead.

• 6013 aluminum is a high-strength aluminum that doesn’t typically use lead.

• 4140 steel, 304 steel, and 303 steel are machinable steels without lead.

Regulations

• California Proposition 65: any product sold in the state that contains lead needs to have a label that says it contains lead.

• California AB 1953: lead content limits for water supply lines.

• RoHS: only 0.1% of lead is allowed, but exemption 6 allows for alloys of aluminum and steel to contain 0.35% (steel) and 0.4% (aluminum) lead content by weight for machining purposes. These exemptions expire between 2021 and 2024.

Lead-containing alloys

• The popular 6061 aluminum that’s used in most machine shops is allowed to have up to 0.15% lead. Not a huge amount, but it’s enough to get a Prop. 65 warning slapped on it at McMaster-Carr.

• Even 6020 aluminum that was developed as a lead-free alternative to 6061 has enough lead content for Prop. 65.

• 7075 aluminum for aircraft has lead.

• Almost all brass has lead in it.

• Steel alloys with “L” in their name are leaded.