Free-machining aluminum alloy extruded material with reduced surface roughness and excellent productivity

Abstract

To obtain an Al—Mg—Si based aluminum alloy extruded material with a smooth surface and no burning without inhibiting the productivity. An aluminum alloy billet includes: Si: 2.0 to 6.0% by mass; Mg: 0.3 to 1.2% by mass; and Ti: 0.01 to 0.2% by mass, a Fe content being restricted to 0.2% or less by mass, with the balance being Al and inevitable impurities. The aluminum alloy billet is subjected to a homogenization treatment by keeping at 500 to 550° C. for 4 to 15 hours. The billet is forcibly cooled to 250° C. or lower at an average cooling rate of 50° C./hr or higher. Then, the billet is subjected to hot-extruding at an extrusion rate of 3 to 10 m/min by being heating at 450 to 500° C. The extruded material is forcibly cooled at an average cooling rate of 50° C./sec or higher and then subjected to an aging treatment. The extruded material can be manufactured that has its surface having a ten-point average roughness Rz of 80 μm or less.