Method for Preparing Nano-SiO2 Reinforced Aluminum Matrix Composites

Abstract

A method for preparing nano-SiO.sub.2 reinforced aluminum matrix composites, includes the following: Step-1, powder mixing: mixing aluminum matrix powder with nano-SiO.sub.2 powder to obtain raw material powder, wherein the aluminum matrix powder has an average particle size between 30 m to 100 m, the nano-SiO.sub.2 powder has an average particle size between 5 nm to 145 nm, mass percentage of nano-SiO.sub.2 in the raw material powder is 0.01% to 5% and the remaining raw material powder is the aluminum matrix powder; Step-2, shaping: press shaping the powder obtained in the Step-1 to obtain base bodies; Step-3, sintering: sintering the base bodies obtained in the Step-2 in an atmosphere of N.sub.2 at 550 C. to 660 C., preserving the temperature for a period of 5 min to 60 min, and cooling in a furnace at end of the period under protection of N.sub.2 for 0.5 h to 3 h; and Step-4, heat treatment.

Claims

1. A method for preparing nano-SiO.sub.2 reinforced aluminum matrix composites, comprising the following steps of: Step-1, powder mixing: mixing aluminum matrix powder with nano-SiO.sub.2 powder to obtain raw material powder, the raw material powder being uniformly mixed, wherein the aluminum matrix powder has an average particle size between 30 m to 100 m, the nano-SiO.sub.2 powder has an average particle size between 5 nm to 145 nm, mass percentage of nano-SiO.sub.2 in the raw material powder is 0.01% to 5% and remaining of the raw material powder is the aluminum matrix powder, and the aluminum matrix powder is elemental aluminum powder, aluminum alloy powder, or aluminum matrix composite powder; Step-2, shaping: press shaping the powder obtained in the Step-1 to obtain base bodies; Step-3, sintering: sintering the base bodies obtained in the Step-2 in an atmosphere of N2 at 550 C. to 660 C., preserving the temperature for a period of 5 min to 60 min, and cooling in a furnace at end of the period under protection of N2 for 0.5 h to 3 h; and Step-4: successively performing solid solution and artificial aging heat treatment on the sintered blanks of the Step-3, where the temperature for the solid solution is 450 C. to 580 C., the time for the solid solution is 0.5 h to 6 h, the temperature for the artificial aging is 100 C. to 200 C. and the time for the artificial aging is 3 h to 24 h.

2. The method of claim 1, wherein in the Step-1, the average particle size of the aluminum matrix powder is 60 m to 80 m, the average particle size of the nano-SiO.sub.2 powder is 10 nm to 50 nm, the mass percentage of the nano-SiO.sub.2 powder in the raw material powder is 0.1% to 1.5%.

3. The method of claim 1, wherein the powder mixing in the Step-1 is done by a ball mill, a rotation speed of the ball mill is 180 r/min to 230 r/min, and the time for ball milling is 4 h to 8 h.

4. The method of claim 3, wherein the rotation speed of the ball mill is 180 r/min to 210 r/min, and the time for ball milling is 5 h to 6 h.

5. The method of claim 1, wherein the nano-SiO.sub.2 powder in the Step-1 is hydrophobic gas-phase silicon dioxide having main parameters shown in the following table: TABLE-US-00012 Property Unit Typical value Specific surface area (BET) m.sup.2/g 110 20 Bulk density* g/l 50 in accordance with DIN EN ISO 787/11, August 1983 Carbon Wt. % 0.6~1.2 Average particle size of primary nm 16 particles Moisture content: dried for 2 h at 105 C. Wt. % 0.5 Loss on ignition: the material dried for Wt. % 2.0 2 h at 105 C. is burnt for 2 h at 1000 C. pH value: in a 4% dispersoid Wt. % 3.6-4.4 SiO.sub.2 content: for the burnt material Wt. % 99.8

6. The method of claim 1, wherein in the powder mixing of the Step-1, a lubricant is added in the raw material powder, wherein the mass of the lubricant is 0.5% to 2% of the mass of the raw material powder.

7. The method of claim 6, wherein the lubricant is added manually or by a mixer, wherein the mixer is any one of a ball mill, a V-type mixer, a conical mixer, a barrel mixer and a helical mixer.

8. The method of claim 6 or claim 7, wherein the base bodies are dewaxed for 20 min to 50 min at 350 C. to 450 C. before the sintering in the Step-3.

9. The method of claim 1, wherein in the Step-2, the press shaping method of the raw material powder is die shaping, and the pressure for shaping is 150 MPa to 500 MPa.

10. The method of claim 1, wherein the Step-4 will not be performed when the sinter is an elemental aluminum matrix or a non-heat-treatable aluminum alloy matrix.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 is a micro-topography of nano-SiO.sub.2 particles according to Embodiment 2 of the present invention;

[0023] FIG. 2 is a fracture topography of a sinter according to Embodiment 2 of the present invention; and

[0024] FIG. 3 is a micro-topography of mixed powder according to Embodiment 7 of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0025] The specific implementations of the present invention will be further described in detail by embodiments with reference to the accompanying drawings.

Embodiment 1

[0026] In this embodiment, the method for preparing nano-SiO.sub.2 reinforced aluminum matrix composites is described by taking a pure aluminum matrix as example. The method specifically includes the following steps.

[0027] Step-1, powder mixing: elemental aluminum powder having an average particle size of 60 m and nano-SiO.sub.2 powder having an average particle size of 50 nm were milled by a mortar and mixed uniformly to obtain raw material powder, where the mass percentage of the nano-SiO.sub.2 powder in the raw material powder was 0.01%, and the remaining was the elemental aluminum powder. The nano-SiO.sub.2 powder used in this step may preferably be hydrophobic gas-phase silicon dioxide having main parameters shown in the following table:

TABLE-US-00002 Property Unit Typical value Specific surface area (BET method) m.sup.2/g 110 20 Bulk density* g/l 50 in accordance with DIN EN ISO 787/11, August 1983 Carbon content Wt. % 0.6-1.2 Average particle size of primary nm 16 particles Moisture content: dried for 2 h at Wt. % 0.5 105 C. Ignition loss: the material dried for 2 h Wt. % 2.0 at 105 C. is burnt for 2 h at 1000 C. pH value: in a 4% dispersoid Wt. % 3.6-4.4 SiO.sub.2 content: for the burnt material Wt. % 99.8

[0028] Step-2, shaping: the powder obtained in the step (1) was die-shaped, where the pressure for pressing was 150 MPa and the pressure holding time was 15 s.

[0029] Step-3, sintering: by a tubular furnace and in the atmosphere of high-purity N2, the shaped powder was sintered at 650 C. for 60 min, and then cooled in the furnace at the end of temperature preservation. The sintering environment in this step may preferably have an oxygen content of less than 10 ppm and a dew point of below 40 C.

[0030] By tests, the flow rate of pure aluminum powder without nano-SiO.sub.2 powder was 110 S/50 g, and the flow rate after the addition of 0.01% of nano-SiO.sub.2 powder was 102 S/50 g. The strength of the pure aluminum powder without nano-SiO.sub.2 powder after sintering was 68 MPa, and the strength of the aluminum matrix composite obtained by sintering the pure aluminum powder and 0.01% of nano-SiO.sub.2 powder was 76 MPa.

Embodiment 2

[0031] In this embodiment, the method for preparing nano-SiO.sub.2 reinforced aluminum matrix composites is described by taking a 2014 aluminum alloy matrix as example. The method specifically includes the following steps.

[0032] Step-1, powder mixing: 2014 aluminum alloy powder having an average particle size of 78 m and nano-SiO.sub.2 powder having an average particle size of 16 nm were mixed to obtain raw material powder, and the raw material powder was ball-milled for 4 h by a planetary ball mill at a rotation speed of 180 r/min and mixed uniformly, where the mass percentage of the nano-SiO.sub.2 powder in the raw material powder was 1%, and the remaining was the 2014 aluminum alloy powder. The nano-SiO.sub.2 powder used in this step was preferably hydrophobic gas-phase silicon dioxide having main parameters shown in the following table:

TABLE-US-00003 Property Unit Typical value Specific surface area (BET method) m.sup.2/g 110 20 Bulk density* g/l 50 in accordance with DIN EN ISO 787/11, August 1983 Carbon content Wt. % 0.6-1.2 Average particle size of primary nm 16 particles Moisture content: dried for 2 h at Wt. % 0.5 105 C. Ignition loss: the material dried for 2 h Wt. % 2.0 at 105 C. is burnt for 2 h at 1000 C. pH value: in a 4% dispersoid Wt. % 3.6-4.4 SiO.sub.2 content: for the burnt material Wt. % 99.8

[0033] Step-2, shaping: the powder obtained in the step (1) was uniformly mixed with zinc stearate as a lubricant by a V-type mixer and die-shaped, where the mass percentage of the zinc stearate in the raw material powder was 0.5 wt %, the pressure for pressing was 400 MPa and the pressure holding time was 20 s.

[0034] Step-3, sintering: by a mesh-belt continuous furnace and in the atmosphere of high-purity N2, the shaped powder was dewaxed at 350 C. for 30 min, then sintered at 560 C. for 40 min, and cooled in the furnace at the end of temperature preservation to the room temperature within 2 h by controlling the cooling rate, so as to obtain a sinter. The sintering environment in this step may preferably have an oxygen content of less than 10 ppm and a dew point of below 40 C. As shown in FIG. 2, there were obvious dimples on the fracture surface of the sinter of the nano-SiO.sub.2 reinforced 2014 aluminum alloy composite. It is indicated that the sinter realizes good metallurgical bonding and has high mechanical properties.

[0035] Step-4, Heat treatment: solid solution and artificial aging heat treatment were successively performed on the sinter, where the temperature for the solid solution was 510 C., the time for the solid solution was 1 h, the temperature for the artificial aging was 180 C. and the time for the artificial aging was 15 h.

[0036] By tests, the flow rate of the 2014 aluminum alloy powder without nano-SiO.sub.2 powder was 90 S/50 g, and the flow rate after the addition of 1% of nano-SiO.sub.2 powder was 79 S/50 g. The strength of the 2014 aluminum alloy powder without nano-SiO.sub.2 powder after sintering was 210 MPa, and the strength of the aluminum matrix composite obtained by sintering the 2014 aluminum alloy powder and 1% of nano-SiO.sub.2 powder was 235 MPa.

Embodiment 3

[0037] In this embodiment, the method for preparing nano-SiO.sub.2 reinforced aluminum matrix composites is described by taking a 7039 aluminum alloy matrix as example. The method specifically includes the following steps.

[0038] Step-1, powder mixing: 7039 aluminum alloy powder having an average particle size of 45 m and nano-SiO.sub.2 powder having an average particle size of 10 nm were mixed to obtain raw material powder, and the raw material powder was ball-milled for 4.5 h by a planetary ball mill at a rotation speed of 185 r/min and mixed uniformly, where the mass percentage of the nano-SiO.sub.2 powder in the raw material powder was 1.5%, and the remaining was the 7039 aluminum alloy powder. The nano-SiO.sub.2 powder used in this step was preferably hydrophobic gas-phase silicon dioxide having main parameters shown in the following table:

TABLE-US-00004 Property Unit Typical value Specific surface area (BET method) m.sup.2/g 110 20 Bulk density* g/l 50 in accordance with DIN EN ISO 787/11, August 1983 Carbon content Wt. % 0.6-1.2 Average particle size of primary nm 16 particles Moisture content: dried for 2 h at Wt. % 0.5 105 C. Ignition loss: the material dried for 2 h Wt. % 2.0 at 105 C. is burnt for 2 h at 1000 C. pH value: in a 4% dispersoid Wt. % 3.6-4.4 SiO.sub.2 content: for the burnt material Wt. % 99.8

[0039] Step-2, shaping: the powder obtained in the step (1) is uniformly mixed with zinc stearate as a lubricant by a helical mixer and die-shaped, where the mass percentage of the zinc stearate in the raw material powder was 0.8%, the pressure for pressing was 180 MPa and the pressure holding time was 15 s.

[0040] Step-3, sintering: by a mesh-belt continuous furnace and in the atmosphere of high-purity N.sub.2, the shaped powder was dewaxed at 350 C. for 22 min, then sintered at 550 C. for 5 min, and cooled in the furnace at the end of temperature preservation to the room temperature within 0.5 h by controlling the cooling rate, so as to obtain a sinter. The sintering environment in this step may preferably have an oxygen content of less than 10 ppm and a dew point of below 40 C.

[0041] Step-4, Heat treatment: solid solution and artificial aging heat treatment were successively performed on the sinter, where the temperature for the solid solution was 450 C., the time for the solid solution was 0.8 h, the temperature for the artificial aging was 150 C. and the time for the artificial aging was 3 h.

[0042] By tests, the flow rate of the 4039 aluminum alloy powder without nano-SiO.sub.2 powder was 92 S/50 g, and the flow rate after the addition of 1.5% of nano-SiO.sub.2 powder was 86 S/50 g. The strength of the 7039 aluminum alloy powder without nano-SiO.sub.2 powder after sintering was 134 MPa, and the strength of the aluminum matrix composite obtained by sintering the 7039 aluminum alloy powder and 1.5% of nano-SiO.sub.2 powder was 143 MPa.

Embodiment 4

[0043] In this embodiment, the method for preparing nano-SiO.sub.2 reinforced aluminum matrix composites is described by taking a 6061 aluminum alloy matrix as example. The method specifically includes the following steps.

[0044] Step-1, powder mixing: 6061 aluminum alloy powder having an average particle size of 80 m and nano-SiO.sub.2 powder having an average particle size of 5 nm were mixed to obtain raw material powder, where the mass percentage of the nano-SiO.sub.2 powder in the raw material powder was 5%, and the remaining was the 6061 aluminum alloy powder. The raw material powder was ball-milled for 5 h by a planetary ball mill at a rotation speed of 180 r/min. At 0.5 h before the end of ball milling, stearic acid having a mass percentage of 1.5% in the raw material powder was added in the raw material powder as a lubricant. At the end of ball milling, mixed powder was obtained. The nano-SiO.sub.2 powder used in this step may be preferably hydrophobic gas-phase silicon dioxide having main parameters shown in the following table:

TABLE-US-00005 Property Unit Typical value Specific surface area (BET method) m.sup.2/g 110 20 Bulk density* g/l 50 in accordance with DIN EN ISO 787/11, August 1983 Carbon content Wt. % 0.6-1.2 Average particle size of primary nm 16 particles Moisture content: dried for 2 h at Wt. % 0.5 105 C. Ignition loss: the material dried for 2 h Wt. % 2.0 at 105 C. is burnt for 2 h at 1000 C. pH value: in a 4% dispersoid Wt. % 3.6-4.4 SiO.sub.2 content: for the burnt material Wt. % 99.8

[0045] Step-2, shaping: the powder obtained in the step (1) was die-shaped, where the pressure for pressing was 200 MPa and the pressure holding time is 10 s.

[0046] Step-3, sintering: by a pusher continuous furnace, in the atmosphere of high-purity N.sub.2 and in a sintering environment having an oxygen content of less than 10 ppm and a dew point of below 40 C., the shaped powder was dewaxed at 450 C. for 20 min, then sintered at 590 C. for 60 min, and cooled in the furnace at the end of temperature preservation to the room temperature within 3 h by controlling the cooling rate, so as to obtain a sinter. The sintering environment in this step preferably had an oxygen content of less than 10 ppm and a dew point of below 40 C.

[0047] Step-4, Heat treatment: solid solution and artificial aging heat treatment were successively performed on the sinter, where the temperature for the solid solution was 580 C., the time for the solid solution was 0.5 h, the temperature for the artificial aging was 160 C. and the time for the artificial aging was 24 h.

[0048] By tests, the flow rate of the 6061 aluminum alloy powder without nano-SiO.sub.2 powder was 93 S/50 g, and the flow rate after the addition of 5% of nano-SiO.sub.2 powder was 84 S/50 g. The strength of the 6061 aluminum alloy powder without nano-SiO.sub.2 powder after sintering was 127 MPa, and the strength of the aluminum matrix composite obtained by sintering the 6061 aluminum alloy powder and 5% of nano-SiO.sub.2 powder was 151 MPa.

Embodiment 5

[0049] In this embodiment, the method for preparing nano-SiO.sub.2 reinforced aluminum matrix composites is described by taking a 6061 aluminum alloy matrix as example. The method specifically includes the following steps.

[0050] Step-1, powder mixing: 6061 aluminum alloy powder having an average particle size of 75 m and nano-SiO.sub.2 powder having an average particle size of 35 nm were mixed to obtain raw material powder, where the mass percentage of the nano-SiO.sub.2 powder in the raw material powder was 1.2%, and the remaining was the 6061 aluminum alloy powder. The raw material powder was ball-milled for 5.5 h by a planetary ball mill at a rotation speed of 185 r/min. At 0.5 h before the end of ball milling, stearic acid having a mass percentage of 1.8% in the raw material powder was added in the raw material powder as a lubricant. At the end of ball milling, mixed powder was obtained. The nano-SiO.sub.2 powder used in this step may preferably be hydrophobic gas-phase silicon dioxide having main parameters shown in the following table:

TABLE-US-00006 Property Unit Typical value Specific surface area (BET method) m.sup.2/g 110 20 Bulk density* g/l 50 in accordance with DIN EN ISO 787/11, August 1983 Carbon content Wt. % 0.6-1.2 Average particle size of primary nm 16 particles Moisture content: dried for 2 h at Wt. % 0.5 105 C. Ignition loss: the material dried for 2 h Wt. % 2.0 at 105 C. is burnt for 2 h at 1000 C. pH value: in a 4% dispersoid Wt. % 3.6-4.4 SiO.sub.2 content: for the burnt material Wt. % 99.8

[0051] Step-2, shaping: the powder obtained in the step (1) was die-shaped, where the pressure for pressing was 350 MPa and the pressure holding time is 25 s.

[0052] Step-3, sintering: by a pusher continuous furnace, in the atmosphere of high-purity N.sub.2 and in a sintering environment having an oxygen content of less than 10 ppm and a dew point of below 40 C., the shaped powder was dewaxed at 370 C. for 45 min, then sintered at 660 C. for 55 min, and cooled in the furnace at the end of temperature preservation to the room temperature within 2.5 h by controlling the cooling rate, so as to obtain a sinter. The sintering environment in this step preferably had an oxygen content of less than 10 ppm and a dew point of below 40 C.

[0053] Step-4, Heat treatment: solid solution and artificial aging heat treatment were successively performed on the sinter, where the temperature for the solid solution was 550 C., the time for the solid solution was 3.5 h, the temperature for the artificial aging was 200 C. and the time for the artificial aging was 15 h.

[0054] By tests, the flow rate of the 6061 aluminum alloy powder without nano-SiO.sub.2 powder was 95 S/50 g, and the flow rate after the addition of 1.2% of nano-SiO.sub.2 powder was 82 S/50 g. The strength of the 6061 aluminum alloy powder without nano-SiO.sub.2 powder after sintering was 193 MPa, and the strength of the aluminum matrix composite obtained by sintering the 6061 aluminum alloy powder and 1.2% of nano-SiO.sub.2 powder was 209 MPa.

Embodiment 6

[0055] In this embodiment, the method for preparing nano-SiO.sub.2 reinforced aluminum matrix composites is described by taking a 7075 aluminum alloy matrix as example. The method specifically includes the following steps.

[0056] Step-1, powder mixing: 7075 aluminum alloy powder having an average particle size of 100 m and nano-SiO.sub.2 powder having an average particle size of 8 nm were mixed to obtain raw material powder, where the mass percentage of the nano-SiO.sub.2 powder in the raw material powder was 0.5%, and the remaining was the 7075 aluminum alloy powder. The raw material powder was ball-milled for 5 h by a planetary ball mill at a rotation speed of 200 r/min. At 0.5 h before the end of ball milling, paraffin having a mass percentage of 2% in the raw material powder was added in the raw material powder as a lubricant. At the end of ball milling, mixed powder was obtained. The nano-SiO.sub.2 powder used in this step may preferably be hydrophobic gas-phase silicon dioxide having main parameters shown in the following table:

TABLE-US-00007 Property Unit Typical value Specific surface area (BET method) m.sup.2/g 110 20 Bulk density* g/l 50 in accordance with DIN EN ISO 787/11, August 1983 Carbon content Wt. % 0.6-1.2 Average particle size of primary nm 16 particles Moisture content: dried for 2 h at Wt. % 0.5 105 C. Ignition loss: the material dried for 2 h Wt. % 2.0 at 105 C. is burnt for 2 h at 1000 C. pH value: in a 4% dispersoid Wt. % 3.6-4.4 SiO.sub.2 content: for the burnt material Wt. % 99.8

[0057] Step-2, shaping: the powder obtained in the step (1) was die-shaped, where the pressure for pressing was 450 MPa and the pressure holding time is 30 s.

[0058] Step-3, sintering: by a pusher continuous furnace and in the atmosphere of high-purity N2, the shaped powder was dewaxed at 350 C. for 50 min, then sintered at 620 C. for 30 min, and cooled in the furnace at the end of temperature preservation to the room temperature within 3 h by controlling the cooling rate, so as to obtain a sinter. The sintering environment in this step may preferably have an oxygen content of less than 10 ppm and a dew point of below 40 C.

[0059] Step-4, Heat treatment: solid solution and artificial aging heat treatment were successively performed on the sinter, where the temperature for the solid solution was 460 C., the time for the solid solution was 6 h, the temperature for the artificial aging was 100 C. and the time for the artificial aging was 8 h.

[0060] By tests, the flow rate of the 7075 aluminum alloy powder without nano-SiO.sub.2 powder was 98 S/50 g, and the flow rate after the addition of 0.5% of nano-SiO.sub.2 powder was 85 S/50 g. The strength of the 7075 aluminum alloy powder without nano-SiO.sub.2 powder after sintering was 241 MPa, and the strength of the aluminum matrix composite obtained by sintering the 7075 aluminum alloy powder and 0.5% of nano-SiO.sub.2 powder was 282 MPa.

Embodiment 7

[0061] In this embodiment, the method for preparing nano-SiO.sub.2 reinforced aluminum matrix composites is described by taking a high-silicon aluminum alloy 4A11 matrix as example. The method specifically includes the following steps.

[0062] Step-1, powder mixing: 4A11 aluminum alloy powder having an average particle size of 30 m and nano-SiO.sub.2 powder having an average particle size of 145 nm were mixed to obtain raw material powder, where the mass percentage of the nano-SiO.sub.2 powder in the raw material powder was 0.08%, and the remaining was the 4A11 aluminum alloy powder. The raw material powder was ball-milled for 6 h by a planetary ball mill at a rotation speed of 200 r/min. At 0.5 h before the end of ball milling, stearic acid having a mass percentage of 1.5% in the raw material powder was added in the raw material powder. At the end of ball milling, mixed powder was obtained. The nano-SiO.sub.2 powder used in this step may preferably be hydrophobic gas-phase silicon dioxide having main parameters shown in the following table:

TABLE-US-00008 Property Unit Typical value Specific surface area (BET method) m.sup.2/g 110 20 Bulk density* g/l 50 in accordance with DIN EN ISO 787/11, August 1983 Carbon content Wt. % 0.6-1.2 Average particle size of primary nm 16 particles Moisture content: dried for 2 h at Wt. % 0.5 105 C. Ignition loss: the material dried for 2 h Wt. % 2.0 at 105 C. is burnt for 2 h at 1000 C. pH value: in a 4% dispersoid Wt. % 3.6-4.4 SiO.sub.2 content: for the burnt material Wt. % 99.8

[0063] Step-2, shaping: the powder obtained in the step (1) was die-shaped, where the pressure for pressing was 250 MPa and the pressure holding time is 10 s.

[0064] Step-3, sintering: by a tubular furnace and in the atmosphere of high-purity N2, the shaped powder was dewaxed at 400 C. for 35 min, then sintered at 610 C. for 50 min, and cooled in the furnace at the end of temperature preservation to the room temperature within 1 h by controlling the cooling rate, so as to obtain a sinter. The sintering environment in this step may preferably have an oxygen content of less than 10 ppm and a dew point of below 40 C.

[0065] Step-4, Heat treatment: solid solution and artificial aging heat treatment were successively performed on the sinter, where the temperature for the solid solution was 525 C., the time for the solid solution was 1.5 h, the temperature for the artificial aging was 175 C. and the time for the artificial aging was 10 h.

[0066] By tests, the flow rate of the 4A11 aluminum alloy powder without nano-SiO.sub.2 powder was 103 S/50 g, and the flow rate after the addition of 0.08% of nano-SiO.sub.2 powder was 97 S/50 g. The strength of the 4A11 aluminum alloy powder without nano-SiO.sub.2 powder after sintering was 186 MPa, and the strength of the aluminum matrix composite obtained by sintering the 4A11 aluminum alloy powder and 0.08% of nano-SiO.sub.2 powder was 198 MPa.

Embodiment 8

[0067] In this embodiment, the method for preparing nano-SiO.sub.2 reinforced aluminum matrix composites is described by taking a high-silicon aluminum alloy Al-10Si matrix as example. The method specifically includes the following steps.

[0068] Step-1, powder mixing: Al-10Si aluminum alloy powder having an average particle size of 50 m and nano-SiO.sub.2 powder having an average particle size of 100 nm were mixed to obtain raw material powder, where the mass percentage of the nano-SiO.sub.2 powder in the raw material powder was 0.05%, and the remaining was the Al-10Si aluminum alloy powder. The raw material powder was ball-milled for 8 h by a planetary ball mill at a rotation speed of 230 r/min. At 0.5 h before the end of ball milling, paraffin having a mass percentage of 1.5% in the raw material powder was added in the raw material powder as a lubricant. At the end of ball milling, mixed powder was obtained. The nano-SiO.sub.2 powder used in this step may preferably be hydrophobic gas-phase silicon dioxide having main parameters shown in the following table:

TABLE-US-00009 Property Unit Typical value Specific surface area (BET method) m.sup.2/g 110 20 Bulk density* g/l 50 in accordance with DIN EN ISO 787/11, August 1983 Carbon content Wt. % 0.6-1.2 Average particle size of primary nm 16 particles Moisture content: dried for 2 h at Wt. % 0.5 105 C. Ignition loss: the material dried for 2 h Wt. % 2.0 at 105 C. is burnt for 2 h at 1000 C. pH value: in a 4% dispersoid Wt. % 3.6-4.4 SiO.sub.2 content: for the burnt material Wt. % 99.8

[0069] Step-2, shaping: the powder obtained in the step (1) was die-shaped, where the pressure for pressing was 250 MPa and the pressure holding time is 10 s.

[0070] Step-3, sintering: by a mesh-belt continuous furnace and in the atmosphere of high-purity N.sub.2, the shaped powder was dewaxed at 380 C. for 40 min, then sintered at 595 C. for 45 min, and cooled in the furnace at the end of temperature preservation to the room temperature within 3 h by controlling the cooling rate, so as to obtain a sinter. The sintering environment in this step may preferably have an oxygen content of less than 10 ppm and a dew point of below 40 C.

[0071] Step-4, Heat treatment: solid solution and artificial aging heat treatment were successively performed on the sinter, where the temperature for the solid solution was 520 C., the time for the solid solution was 2 h, the temperature for the artificial aging was 170 C. and the time for the artificial aging was 10 h.

[0072] By tests, the flow rate of the Al-10Si aluminum alloy powder without nano-SiO.sub.2 powder was 107 S/50 g, and the flow rate after the addition of 0.05% of nano-SiO.sub.2 powder was 95 S/50 g. The strength of the Al-10Si aluminum alloy powder without nano-SiO.sub.2 powder after sintering was 130 MPa, and the strength of the aluminum matrix composite obtained by sintering the Al-10Si aluminum alloy powder and 0.05% of nano-SiO.sub.2 powder was 145 MPa.

Embodiment 9

[0073] In this embodiment, the method for preparing nano-SiO.sub.2 reinforced aluminum matrix composites is described by taking a ceramic particle reinforced Al2O3-2024 aluminum matrix composite as example. The method specifically includes the following steps.

[0074] Step-1, powder mixing: Al2O3-2024 aluminum matrix composite powder having an average particle size of 85 m and nano-SiO.sub.2 powder having an average particle size of 15 nm were mixed to obtain raw material powder, where the mass percentage of the nano-SiO.sub.2 powder in the raw material powder was 0.1%, and the remaining was the Al2O3-2024 aluminum matrix composite powder. The raw material powder was ball-milled for 7 h by a planetary ball mill at a rotation speed of 210 r/min. At 0.5 h before the end of ball milling, zinc stearate having a mass percentage of 1% in the raw material powder was added in the raw material powder as a lubricant. At the end of ball milling, mixed powder was obtained. As shown in FIG. 3, it could be known that, by uniformly mixing Al2O3-2024 aluminum matrix composite powder with the nano-SiO.sub.2 powder, the nano-SiO.sub.2 particles could be well bonded with the matrix after sintering, so that the mechanical properties were significantly enhanced. The nano-SiO.sub.2 powder used in this step may preferably be hydrophobic gas-phase silicon dioxide having main parameters shown in the following table:

TABLE-US-00010 Property Unit Typical value Specific surface area (BET method) m.sup.2/g 110 20 Bulk density* g/l 50 in accordance with DIN EN ISO 787/11, August 1983 Carbon content Wt. % 0.6-1.2 Average particle size of primary nm 16 particles Moisture content: dried for 2 h at Wt. % 0.5 105 C. Ignition loss: the material dried for 2 h Wt. % 2.0 at 105 C. is burnt for 2 h at 1000 C. pH value: in a 4% dispersoid Wt. % 3.6-4.4 SiO.sub.2 content: for the burnt material Wt. % 99.8

[0075] Step-2, shaping: the powder obtained in the step (1) was die-shaped, where the pressure for pressing was 300 MPa and the pressure holding time is 20 s.

[0076] Step-3, sintering: by a mesh-belt continuous furnace and in the atmosphere of high-purity N2, the shaped powder was dewaxed at 440 C. for 25 min, then sintered at 585 C. for 40 min, and cooled in the furnace at the end of temperature preservation to the room temperature within 2 h by controlling the cooling rate, so as to obtain a sinter. The sintering environment in this step may preferably have an oxygen content of less than 10 ppm and a dew point of below 40 C.

[0077] Step-4, Heat treatment: solid solution and artificial aging heat treatment were performed on the sinter, where the temperature for the solid solution was 490 C., the time for the solid solution was 1 h, the temperature for the artificial aging was 190 C. and the time for the artificial aging was 20 h.

[0078] By tests, the flow rate of the Al2O3-2024 aluminum matrix composite powder without nano-SiO.sub.2 powder was 94 S/50 g, and the flow rate after the addition of 0.1% of nano-SiO.sub.2 powder was 81 S/50 g. The strength of the Al2O3-2024 aluminum matrix composite powder without nano-SiO.sub.2 powder after sintering was 226 MPa, and the strength of the aluminum matrix composite obtained by sintering the Al2O3-2024 aluminum matrix composite powder and 0.1% of nano-SiO.sub.2 powder was 257 MPa.

Embodiment 10

[0079] In this embodiment, the method for preparing nano-SiO.sub.2 reinforced aluminum matrix composites is described by taking a non-heat-treatable 3003 aluminum alloy matrix as example. The method specifically includes the following steps.

[0080] Step-1, powder mixing: 3003 aluminum alloy powder having an average particle size of 70 m and nano-SiO.sub.2 powder having an average particle size of 70 nm were mixed to obtain raw material powder, where the mass percentage of the nano-SiO.sub.2 powder in the raw material powder was 0.4%, and the remaining was the 3003 aluminum alloy powder. The raw material powder was ball-milled for 4 h by a planetary ball mill at a rotation speed of 190 r/min. At 0.5 h before the end of ball milling, paraffin having a mass percentage of 1.5% in the raw material powder was added in the raw material powder as a lubricant. At the end of ball milling, mixed powder was obtained. The nano-SiO.sub.2 powder used in this step may preferably be hydrophobic gas-phase silicon dioxide having main parameters shown in the following table:

TABLE-US-00011 Property Unit Typical value Specific surface area (BET method) m.sup.2/g 110 20 Bulk density* g/l 50 in accordance with DIN EN ISO 787/11, August 1983 Carbon content Wt. % 0.6-1.2 Average particle size of primary nm 16 particles Moisture content: dried for 2 h at Wt. % 0.5 105 C. Ignition loss: the material dried for 2 h Wt. % 2.0 at 105 C. is burnt for 2 h at 1000 C. pH value: in a 4% dispersoid Wt. % 3.6-4.4 SiO.sub.2 content: for the burnt material Wt. % 99.8

[0081] Step-2, shaping: the powder obtained in the step (1) was die-shaped, where the pressure for pressing was 500 MPa and the pressure holding time is 10 s.

[0082] Step-3, sintering: by a pusher continuous furnace and in the atmosphere of high-purity N2, the shaped powder was dewaxed at 400 C. for 30 min, then sintered at 570 C. for 40 min, and cooled in the furnace at the end of temperature preservation to the room temperature within 3 h by controlling the cooling rate, so as to obtain a sinter. The sintering environment in this step may preferably have an oxygen content of less than 10 ppm and a dew point of below 40 C.

[0083] By tests, the flow rate of the 3003 aluminum alloy powder without nano-SiO.sub.2 powder was 91 S/50 g, and the flow rate after the addition of 0.4% of nano-SiO.sub.2 powder was 78 S/50 g. The strength of the 3003 aluminum alloy powder without nano-SiO.sub.2 powder after sintering was 112 MPa, and the strength of the aluminum matrix composite obtained by sintering the 3003 aluminum alloy powder and 0.4% of nano-SiO.sub.2 powder was 140 MPa.