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.

1 . An Al—Si—Mg based aluminum alloy extruded material comprising:
 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, 
 wherein 
 the number of AlFeSi particles having a diameter of 5 μm or more is 20 or less per 50 μm square area of the extruded material, 
 the number of Mg 2 Si particles having a diameter of 2 μm or more is 20 or less per 50 μm square area of the extruded material, and 
 a ten-point average roughness Rz of a surface of the extruded material is 80 μm or less. 
 
     
     
         2 . The Al—Si—Mg based aluminum alloy extruded material according to  claim 1 , further comprising one or more kinds of:
 Mn: 0.1 to 1.0% by mass; and 
 Cu: 0.1 to 0.4% by mass. 
 
     
     
         3 . The Al—Si—Mg based aluminum alloy extruded material according to  claim 1 , further comprising one or more kinds of:
 Cr: 0.03 to 0.1% by mass; and 
 Zr: 0.03 to 0.1% by mass. 
 
     
     
         4 . The Al—Si—Mg based aluminum alloy extruded material according to  claim 2 , further comprising one or more kinds of:
 Cr: 0.03 to 0.1% by mass; and 
 Zr: 0.03 to 0.1% by mass. 
 
     
     
         5 - 8 . (canceled)