Lead-free free-cutting magnesium brass alloy and its manufacturing method

Abstract

A lead-free free-cutting magnesium brass alloy comprises 56.0 to 64.0 wt % Cu, 0.6 to 2.5 wt % Mg, 0.15 to 0.4 wt % P and other elements 0.002 to 0.9 wt % which comprise at least two elements selected from the group consisting of Al, Si, Sb, Sn, Re, Ti and B and the balance being Zn and unavoidable impurities. The process for producing such alloy is also proposed. The invented alloy is excellent in cuttability, castability, hot and cold workability, corrosion resistance, mechanical properties and weldability and particularly applicable in spare parts, forging and castings which need cutting, grinding and electroplating process. The cost of necessary metal materials of the invented alloy is lower than lead-free free-cutting bismuth and antimony brass alloy and is equivalent to lead-contained brass alloy.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application is a continuation of U.S. patent application Ser. No. 12 / 207,136 filed on Sep. 9, 2008, which claims priority from Chinese Patent Application No. 200810110818.3 filed Jun. 11, 2008.FIELD OF THE INVENTION[0002]The present invention generally relates to a magnesium brass alloy, especially a lead-free free-cutting magnesium brass alloy which is applicable in spare parts for a water supply system.BACKGROUND OF THE INVENTION[0003]It is well-known that lead-containing brass alloys such as CuZn40Pb1, C36000, C3604 and C3771 usually contain 1.0-3.7 wt % Pb for ensuring excellent free-cuttability.[0004]Lead-containing brass alloys are still widely used in the manufacture of many products due to their excellent cuttability and low cost. However, Pb-contaminated steam produced by the process of smelting and casting lead-contained brass alloy and Pb-contaminated dust produced in the process of cutting and grinding the lead-contained ...

AI Technical Summary

Benefits of technology

[0012]The invented alloy is in the base of alpha-beta brass and realizes excellent cuttability by the fracture of intermetallic compounds Cu2Mg which is formed from element Mg and Cu.

[0024]The advantages of the invented alloy are as follows. Smelting is processing in the atmosphere when the metals are protected with the covering agent. The addition of easily oxidized and volatile Mg is not effected by the addition of a conventional Cu—Mg master alloy or pure magnesium, but rather by Mg-based alloy whose melting point is lower than pure magnesium and boiling point is higher than pure magnesium. This reduces the consumption of Mg and is better to control the addition of Mg. Casting ingots rather than extruding bars are used to disposably form spare parts with complex structures for water supply systems by precision die forging. It could take out extruding process and save manufacturing cost. By die forging and extruding with an elongation coefficient greater than 30, the intermetallic compounds Cu2Mg and grain are further refined and dispersed uniformly thereby improving the mechanical properties of the invented alloy. The manufacturing method of the invented alloy is easy to carry out. And the equipments for production are the same as Pb-contained brass alloy.

Problems solved by technology

However, Pb-contaminated steam produced by the process of smelting and casting lead-contained brass alloy and Pb-contaminated dust produced in the process of cutting and grinding the lead-contained brass alloy are harmful to the human body and the environment.

If the lead-containing brass alloys are used in drinking-water installations such as faucets, valves and bushings, contamination of the drinking water by Pb is unavoidable.

In addition, toys which are produced by Pb-containing brass alloys are more harmful, as they are touched frequently, thus increasing potential exposure to Pb.

Ingestion of lead by humans is harmful, so the use of lead is being strictly banned by law in many countries due to the concerns on health and environment.

Some of them use Si instead of Pb, but the cuttability is not remarkably improved and the cost increases due to the high quantity of copper.

Therefore, silicon brass alloys are not commercially competitive at present.

Therefore, these kinds of bismuth brass alloys are not competitively priced.

Considering that bismuth element is expensive, rare in the reserves and has poor cold and hot workability, using a bismuth brass alloy instead of a lead-containing brass alloy may be financially problematic.

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