Casting Densification Process

Reprinted from ALCOA TECHNOLOGY MARKETING DIVISION
Products/Processes/Services TMD Report N.5

Alcoa has developed a method designated the Alcoa 359 Process, which significantly improves the fatigue strength of aluminum sand and permanent mold castings. In achieving this improvement, the process substantially eliminates the microporosity normally encountered in aluminum castings as a result of internal gas and shrinkage. Thus, the method makes possible the salvaging of castings, which have been scrapped for reasons of internal porosity; thereby achieving a significant improvement in recovery. This combination of factors results in a competitive advantage to users of the Alcoa 359 Process.

The technique involves the exposure of aluminum castings to a high isostatic pressure at selected combinations of pressure (15,000 psig), temperature and time. Such treatment eliminates internal gas shrinkage porosity. The resulting high density aluminum castings will meet Class A radiographic specifications, and exhibit higher and more uniform tensile properties. However, the most significant improvement is an increase in fatigue strength approaching that of forgings. This represents an improvement in fatigue strength of up to 300 percent over ordinary cast products, and laboratory tests indicate that these property improvements can be obtained consistently. There is no question about the ability of the process to enable castings to meet Class A x-ray qualifications provided the porosity is internally contained. Table I presents tensile properties of test bars from 7 x 7 x V4-in. permanent mold cast plates comparing untreated castings and castings treated by this process. Table II shows results of tensile and fatigue tests on specimens cut from various production sand and permanent mold castings. Following these is a graph showing rotating beam fatigue curves comparing castings treated by the Alcoa 359 Process to standard permanent mold castings and forgings.

Alcoa’s evaluation of the utilization of this process concluded that diesel pistons constituted a prime potential market for permanent mold castings treated by the Alcoa 359 Process. Obviously, this is not the only market. Any part which benefits from superior fatigue properties could justify the additional expense of this process.

This process is covered by U. S. Patent No. 3,496,624.


Table 1: Tensile properties of bars from 7 x 7 3/4-in. permanent mold plates

Untreated
Treated by Alcoa 359 Process
Alloy
Bar no.
T.S., ksi
Y.S., ksi
% El. in 2 in.
T.S., ksi
Y.S., ksi
% El. in 2 in.
A356-T61 123

4

5

35.634.834.0

33.2

30.2

27.127.327.4

27.3

25.7

4.54.04.0

2.5

2.0

38.837.436.7

36.9

36.4

30.830.730.3

30.1

29.3

4.53.53.0

3.0

3.5

A356-T61 123

4

5

39.837.936.5

35.5

33.6

29.430.329.2

28.5

27.8

6.54.52.5

2.5

3.0

42.742.441.6

41.6

41.2

31.632.631.3

31.6

32.7

10.06.56.5

6.0

6.0

A357-T62 123 43.641.135.5 38.938.3- 1.00.50.5 47.747.246.7 40.842.141.1 3.02.52.0
A357-T62 123 33.028.127.0 31.1– 0.50.50.5 38.835.635.5 34.034.133.6 0.50.50.5

 

Table 2: Results of tensile and fatigue tests on specimens cut from various production sand and permanent mold castings

Part
Alcoa
359
Process
No.
Form, alloy
and temper
Fatigue
cycles a
20 ksi(1)
Tensile Properties
T.S.,
ksi
Y.S.,
ksi
Elong.
%
Control housing Yes D5029A PM, A356-T61 4,653,000 40.5 28.5 9
Control housing Yes D5029B PM, A356-T61 4,646,000 41.5 28.5 12
Control housing No D5028C PM, A356-T61 452,000 38.5 28.0 7
Control housing No D5028D PM, A356-T61 39.039.038.5

38.5

37.5

29.029.529.0

28.0

29.5

888

7

7

Control housing Yes D5029E PM, A356-T61 43.043.043.0

42.5

42.0

31.531.531.5

31.0

31.0

121512

9

9

Fuel Regulator Yes D5029F PM, 356-T6 1,558,000 36.035.534.5 23.523.022.0 986
Fuel Regulator No D5028F PM, 356-T6 355,000 33.533.032.5 22.022.023.0 665
Fuel Regulator Yes D5029G PM, 356-T6 600,000 38.0 24.0 13
Fuel Regulator No D5028G PM, 356-T6 875,000 37.0 22.0 13
Piston Yes D5029J PM, F132-T7 23,107,000 46.5 43.0 0.5
Piston No D5028J PM, F132-T7 191,000 38.0 0.0
Electrical connector Yes D5029K PM, 356-T6 38.038.037.5

36.0

22.523.522.5

21.5

131613

9

Tool plate Yes D5029L PM, 356-T6 3,255,0001,973,0001,928,000 35.535.034.5 24.522.522.5 697
Tool plate No D5028L PM, 356-T6 337,000285,000285,000 32.029.527.0 21.522.023.0 631.5
Meat slicer Yes D5029M PM, A108-F 341,000 28.016.5 13.513.0 40.0
Meat slicer No D5028M PM, A108-F 83,000 24.522.5 15.515.0 1.51.5
Timing gear cover Yes D5029N PM, 333-T7 47.045.044.0 42.041.540.5 1.01.01.0
Timing gear cover No D5028N PM, 333-T7 39.537.536.5 0.00.50.0
Timing gear cover Yes D5029ON PM, 333-T7 43.539.5 41.639.0 1.01.0
Rocket launcher Yes D5029P SC, A356-T61 2,222,0001,739,0001,478,000 42.040.038.0

38.0

31.028.531.5

31.0

10113

2.0

Rocket launcher No D5028P SC, A356-T61 584,000331,00067,000 37.035.534.0

27.0

29.530.028.5

26.5

433

1.5

Transmission case Yes D5029Q SC, C355-T61 2,254,0001,957,000 40.039.539.5 35.535.534.5 1.51.53
Transmission case No D5028Q SC, C355-T61 163,000137,000 33.032.530.5 32.031.5- 0.50.50.5
Transmission case Yes D5029R SC, C355-T61 6,307,0001,101,000 41.040.5 36.035.0 1.51.5
Transmission case No D5028R SC, C355-T61 182,000108,000 39.536.0 33.532.5 2.00.5
Piston Yes D5029S SC, C355-T6 40.0 31.5 4
Piston Yes D5029T SC, C355-T6 36.0 30.5 2.0
Carburetor body Yes D5029U SC, C356-T6 1,534,000 34.033.0 22.522.0 76
Carburetor body No D5028U SC, C356-T6 128,00092,000 29.5 20.5 4
Cylinder Yes D5029V SC, CH70-T7 9,747,000520,000 71.568.5 65.563.0 1211
Cylinder No D5028V SC, CH70-T7 597,000397,000 71.066.0 65.060.5 106
PistonPart no. 433-177(head up) Yes D5029W PM, 142-T4 11,241,0009,452,000 37.036.535.0

34.5

30.030.030.0

29.0

0.00.00.0

0.0

PistonPart no. 433-177(head up) No D5028W PM, 142-T4 980,000437,000 34.034.029.5

29.5

28.529.028.5

28.5

0.00.00.0

0.0

PistonPart no. 433-110(head down) Yes D5029X PM, 142-T4 (2) 36.536.536.0

36.0

29.030.029.5

29.5

0.00.00.0

0.0

PistonPart no. 433-110(head down) No D5028X PM, 142-T4 226,000 35.534.033.5

31.0

30.029.529.5

29.5

0.00.00.0

0.0

PistonPart no. 433-185(VRC) Yes D5029Y VRC, 142-T4 22,629,000(3)20,000,000(3) 41.540.527.0

37.5

28.530.0(4)

30.0

1.51.50.0

0.0

PistonPart no. 433-185(VRC) No D5028Y PM, 142-T4 8,701,0003,575,000 41.040.525.5

24.0

30.029.5(4)

(4)

1.51.50.0

0.0