Lead-free free-cutting silicon brass alloy and preparation method thereof

The invention discloses a lead-free free-cutting silicon brass alloy and a preparation method thereof. The silicon brass alloy comprises the following components and contents: 28-34wt% of zinc, 2.2-3.5wt% of silicon, 0.5-1.8wt% of zinc sulfide and the balance of copper. The lead-free free-cutting silicon brass alloy has the beneficial effects that the copper content in brass alloy is less than 70%, and the free-cutting performance of brass alloy is improved through adjusting the contents of zinc, silicon and zinc sulfide added in brass alloy; the obtained free-cutting brass alloy is low in cost; and zinc sulfide is introduced in silicon brass by using an in-situ synthesis technology and is brittle, so that the effect of improving the cutting performance of brass is achieved.