Sintering of Aluminum and Aluminum Alloys

Conventionally pressed and sintered aluminum powder metal parts have been commercially available for many years. Sintered aluminum P/M parts are competitive with many aluminum castings, extrusions, and screw machine products that require expensive and time-consuming finishing operations. In addition, sintered aluminum P/M parts compete with other metal powder parts in applications where some of the attractive physical and mechanical properties of aluminum can be used.

Commercially available aluminum powder alloy compositions consist of blends of atomized aluminum powders mixed with powders of various alloying elements such as zinc, copper, magnesium, and silicon as follows:

Grade

Composition

%

Cu

Mg

Si

Al

Lubricant

601AB

0.25

1.0

0.6

bal

1.5

201AB

4.4

0.5

0.8

bal

1.5

602AB

0.6

0.4

bal

1.5

202AB

0.6

0.4

bal

1.5

MD-22

2.0

1.0

0.3

bal

1.5

MD-24

4.4

0.5

0.9

bal

1.5

MD-69

0.25

1.0

0.6

bal

1.5

MD-76

1.6

2.5

bal

1.5

Aluminum P/M parts can be sintered in a controlled, inert atmosphere or in vacuum. Sintering temperatures are based on alloy composition and generally range from 595 to 625 °C (1100 to 1160 °F). Sintering time varies from 10 to 30 min. Nitrogen, dissociated ammonia, hydrogen, argon, and vacuum have been used for sintering aluminum; however, nitrogen is preferred because it results in high as-sintered mechanical properties (Table 17). It is also economical in bulk quantities. If a protective atmosphere is used, a dew point of -40 °C (-40 °F) or below is recommended. This is equivalent to a moisture content of 120 mL/m3 (120 ppm) maximum.

Table 17 Typical properties of nitrogen-sintered aluminum P/M alloys

Alloy

Compacting pressure

Green density

Green strength

Sintered density

Temper

Tensile strength^

%

Hardness

MPa tsi

% g/cm3

MPa psi

% g/cm3

MPa

ksi

MPa

ksi

601AB

96 7

85 2.29

3.1 450

91.1 2.45

T1

110

16

48

7

6

55-60 HRH

T4

141

20.5

96

14

5

80-85 HRH

T6

183

26.5

176

25.5

1

70-75 HRE

165 12

90 2.42

6.55 950

93.7 2.52

T1

139

20.1

88

12.7

5

60-65 HRH

T4

172

24.9

114

16.6

5

80-85 HRH

T6

232

33.6

224

32.5

2

75-80 HRE

345 25

95 2.55

10.4 1500

96.0 2.58

T1

145

21

94

13.7

6

65-70 HRH

T4

176

25.6

117

17

6

85-90 HRH

T6

238

34.5

230

33.4

2

80-85 HRE

602AB

165 12

90 2.42

6.55 950

93.0 2.55

T1

121

17.5

59

8.5

9

55-60 HRH

T4

121

17.5

62

9

7

65-70 HRH

T6

179

26

169

24.5

2

55-60 HRE

345 25

95 2.55

10.4 1500

96.0 2.58

T1

131

19

62

9

9

55-60 HRH

T4

134

19.5

65

9.5

10

70-75 HRH

T6

186

27

172

25

3

65-70 HRE

201AB

110 8

85 2.36

4.2 600

91.0 2.53

T1

169

24.5

145

24

2

60-65 HRE

T4

210

30.5

179

26

3

70-75 HRE

T6

248

36

248

36

0

80-85 HRE

180

13

90

2.50

8.3

1200

92.9

2.58

T1

201

29.2

170

24.6

3

70-75 HRE

T4

245

35.6

205

29.8

3.5

75-80 HRE

T6

323

46.8

322

46.7

0.5

85-90 HRE

413

30

95

2.64

13.8

2000

97.0

2.70

T1

209

30.3

181

26.2

3

70-75 HRE

T4

262

38

214

31

5

80-85 HRE

T6

332

48.1

327

47.5

2

90-95 HRE

202AB

180

13

90

2.49

5.4

780

92.4

2.56

T1

160

23.2

75

10.9

10

55-60

Compacts

HRH

T4

194

28.2

119

17.2

8

70-75 HRH

T6

227

33

147

21.3

7.3

45-50 HRE

Cold-

180

13

90

2.49

5.4

780

92.4

2.56

T2

238

33.9

216

31.4

2.3

80 HRE

formed

T4

236

34.3

148

21.5

8

70 HRE

parts

T6

274

39.8

173

25.1

8.7

85 HRE

(19% strain)

T8

280

40.6

250

36.2

3

87 HRE

Tensile properties determined using powder metal flat tension bar (MPIF standard 10-63), sintered 15 min at 620 °C (1150 °F) in nitrogen

Aluminum preforms can be sintered in batch furnaces or continuous radiant tube mesh or cast belt furnaces. Optimum dimensional control is best attained by maintaining furnace temperature at ±2.8 °C (±5 °F). Figure 40 illustrates typical heating cycles for aluminum parts sintered in various furnaces.

Fig. 40 Typical heating cycles for aluminum P/M parts sintered in (a) batch furnace, (b) continuous furnace, and (c) vacuum furnace

Mechanical properties are directly affected by thermal treatment. All compositions respond to solution heat treating, quenching, and aging in the same manner as conventional heat-treatable alloys. Table 18 summarizes some typical properties of aluminum P/M alloys.

Table 18 Typical heat-treated properties of nitrogen-sintered aluminum P/M alloys

Heat-treated variables and properties

Grades

MD-22

MD-24

MD-69

MD-76

Solution treatment

Temperature, °C (°F)

520 (970)

500 (930)

520 (970)

475 (890)

Time, min

30

60

30

60

Atmosphere

Air

Air

Air

Air

Quench medium

H2O

H2O

H2O

H2O

Agmg

Temperature, °C (°F)

150 (300)

150 (300)

150 (300)

125 (257)

Time, h

18

18

18

18

Atmosphere

Air

Air

Air

Air

Heat-treated (T6) properties(a)

Transverse-rupture strength, MPa (ksi)

550 (80)

495 (72)

435 (63)

435 (63)

Yield strength, MPa (ksi)

200 (29)

195 (28)

195 (28)

275 (40)

Tensile strength, MPa (ksi)

260 (38)

240 (35)

205 (30)

310 (45)

Elongation, %

3

3

2

2

Rockwell hardness, HRE

74

72

71

80

Electrical conductivity, %IACS

36

32

39

25

T6, solution heat treated, quenched, and artificially age hardened

T6, solution heat treated, quenched, and artificially age hardened

0 0

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