Method for controlling microstructure of recycled aluminum alloy

Abstract

A method for controlling a microstructure of a recycled aluminum alloy includes steps of: degassing and removing inclusions from the molten aluminum alloy, refining grains and controlling the deformed microstructure. Good microstructures of the deformed aluminum alloy can be obtained after degassing by gas flushing, removing the inclusions by filtering, refining the grains by adding a modifier, and extruding or rolling or forging. The present invention provides desirable results of degassing and impurity removal. Contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.02-0.26 ml/100 g Al and 0.4-0.7 area % metallographic field respectively. In an aluminum alloy billet, an average grain size is 25-50 μm and a short rod-shaped or elliptical second phase is 10-100 nm. In the deformed aluminum alloy, a grain aspect ratio is 10:1-100:1 and short rod-shaped or elliptical particles are 5-80 nm.

What is claimed is: 
     
         1 . A method for controlling a microstructure of a recycled aluminum alloy, comprising steps of:
 (1), adopting aluminum scrap as raw material, and obtaining a target molten aluminum alloy successively through smelting, slagging and composition adjustment;   (2), refining the target molten aluminum alloy obtained in the step (1) with degassing and adding a modifier, so as to obtain a refined recycled molten aluminum alloy; wherein gas of the target molten aluminum alloy is removed by gas flushing, and the modifier is added to achieve grain refinement;   (3), filtering the refined recycled molten aluminum alloy and casting into an aluminum alloy billet; wherein filtering is for removing inclusions;   (4), heating the aluminum alloy billet for homogenization; and   (5), processing the homogenized billet with extruding, rolling or forging, so as to obtain a deformed aluminum alloy.   
     
     
         2 . The method, as recited in  claim 1 , wherein the step (1) particularly comprises steps of: adopting the aluminum scrap as the raw material, smelting at 650-900° C. for 30-300 minutes, removing slag from a molten aluminum alloy, and adjusting compositions of the molten aluminum alloy to target compositions, so as to obtain the target molten aluminum alloy with the target compositions. 
     
     
         3 . The method, as recited in  claim 1 , wherein the step (2) particularly comprises steps of: refining the target molten aluminum alloy with the target compositions with degassing and modifying at 700-900° C. for 10-60 minutes; wherein: degassing is gas flushing by N 2 , Ar, or a mixed gas of N 2  and Ar; for gas flushing, a flow rate is 1-15 L/min, and a pressure is 0.12-0.50 MPa; the modifier is added into the target molten aluminum alloy with an addition amount of 0.5-3.5 kg/t, and is at least one member selected from a group consisting of Al—Ti—B alloy, Al—Ti—C alloy, and Al—Ti—C-RE (RE represents rare earths) alloy; and contents of hydrogen and inclusions in the refined recycled molten aluminum alloy are 0.02-0.26 ml/100 g Al and 0.4-0.7 area % metallographic field respectively. 
     
     
         4 . The method, as recited in  claim 3 , wherein: when gas flushing is made by the mixed gas of N 2  and Ar, a volume ratio of N 2  and Ar is 5:1 to 1:5. 
     
     
         5 . The method, as recited in  claim 1 , wherein the step (3) particularly comprises steps of: filtering the refined recycled molten aluminum alloy with a ceramic filter of 10-60 meshes, and then casting into the aluminum alloy billet, wherein the aluminum alloy billet has an average grain size of 25-50 μm and a short rod-shaped or elliptical second phase of 10-100 nm. 
     
     
         6 . The method, as recited in  claim 1 , wherein the step (4) particularly comprises steps of: homogenizing at 350-500° C. for 8-40 hours. 
     
     
         7 . The method, as recited in  claim 1 , wherein the step (5) particularly comprises steps of: extruding the homogenized billet into a profile at a temperature from room temperature to 500° C. with an extrusion ratio of 4-40 and a billet speed of 0.1-5.0 mm/s, wherein the profile has short rod-shaped or elliptical particles of 5-80 nm with a grain aspect ratio of 20:1-100:1. 
     
     
         8 . The method, as recited in  claim 1 , wherein the step (5) particularly comprises steps of: rolling the homogenized billet into a profile at a temperature from room temperature to 500° C. with reduction of 5-50%, wherein the profile has short rod-shaped or elliptical particles of 5-80 nm with a grain aspect ratio of 10:1-100:1. 
     
     
         9 . The method, as recited in  claim 1 , wherein the step (5) particularly comprises steps of: forging the homogenized billet into a profile at a temperature from room temperature to 500° C. with deformation of 10-50%, wherein the profile has short rod-shaped or elliptical particles of 5-80 nm with a grain aspect ratio of 10:1-100:1.