Magnesium-contained high-silicon aluminum alloys structural materials and manufacture method thereof

Abstract

The magnesium-contained high-silicon aluminum alloys for use as structural materials, including profiles, bars, sheets, and forgings, are manufactured by a process including the steps of: casting an alloy ingot by direct chill casting, preheating the ingot to disperse eutectic Si phase particles, and thermal-plastic processing and heat-treating to obtain the product with a final shape and a modified microstructure. The aluminum alloys contain 0.2˜2.0 wt % of Mg and 8˜18 wt % of Si, and have homogeneous and fine microstructure, wherein the aluminum matrix is equiaxed with an average grain size less than 6 μm, and the silicon and second phase particles are dispersed with an average size less than 5 μm. Without adding any modifiers, they are low-costly produced by incorporating the direct chill casting with thermal-plastic processing and heat treatment, which give rise to good plasticity and relatively high strength.

1 . A process for manufacturing aluminum alloy containing Mg and high silicon, which comprises sectional material, bar, sheet, and forging, comprises the steps of:
 (a) casting an ingot of said aluminum alloys by a method of direct chill casting;   (b) preheat-treating said ingot to disperse eutectic Si phase particles; and   (c) thermal-plastic processing and heat-treating to obtain said aluminum alloys with a final shape and a modified microstructure, wherein the strengthening mechanisms of said aluminum alloys refer to a grain refinement strengthening of aluminum matrix, a dispersion strengthening of silicon particles, and a precipitation strengthening of second phase particles, wherein said aluminum alloys contain 0.2˜2.0 weight percentage (wt %) of Mg, 8˜18 wt % of Si, wherein said aluminum alloys have an evenly refined microstructure, and said aluminum matrix is equiaxed with an average grain size <6 μm, and said silicon and said second phase particles are dispersed with an average size <μm.   
   
   
       2 . The process, as recited in  claim 1 , wherein said alloy of said structural material contains at least one of Cu, Zn, Ni, Ti, and Fe, wherein a total weight percentage of said Cu, Zn, Ni, Ti, and Fe is equal or less than 2 wt %. 
   
   
       3 . The process as recited in  claim 1  wherein, in the step (a), said direct chill casting is performed at a relative casting temperature of 150˜300° C. above the liquidus line of said aluminum alloys, a casting speed of 100˜200 mm/min, and a cooling water flux of 5˜15 g/mm·s on the periphery of said ingot, wherein no modifier is added in said direct chill casting; wherein, in the step (b), said ingot is preheated to disperse eutectic Si phase particles at a heating rate of 10˜30° C./min, a heating temperature of 450˜520° C., and a holding time of 1˜3 hours, wherein said aluminum alloy is cooled naturally or is cooled forcedly, wherein said aluminum alloy is heat-treated after said thermal-plastic processing. 
   
   
       4 . The process, as recited in  claim 3 , wherein the step (c) further comprises a step of solution treatment and a step of artificial aging treatment for said aluminum alloys after said thermal-plastic processing with natural cooling, wherein said solution treatment is performed at a heating rate of 10˜30° C./min, a solution treatment temperature of 500˜540° C., and a solution treatment time of 0.5-3 hours, wherein said artificial aging treatment is performed at an aging temperature of 160˜200° C., and an aging time of 1˜10 hours. 
   
   
       5 . The process, as recited in  claim 3 , wherein the step (c) further comprises a step of artificial or natural aging treatment for forcedly cooling said aluminum alloy after said thermal-plastic processing, wherein said artificial aging treatment is performed at an aging temperature of 160˜200° C., and an aging time of 1˜10 hours. 
   
   
       6 . The process, as recited in  claim 3 , wherein the step (c) further comprises a step of hot rolling in said thermal-plastic processing, wherein a total reduction amount of said hot rolling is greater than 40%. 
   
   
       7 . The process, as recited in  claim 3 , wherein the step (c) further comprises a step of hot extrusion in said thermal-plastic processing, wherein an extrusion ratio of said hot extrusion is greater than 15. 
   
   
       8 . The process, as recited in  claim 3 , wherein the step (c) further comprises a step of hot forging in said thermal-plastic processing, wherein a forging ratio of said hot forging is greater than 40%.