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	1 2 3 4 5	35.6 34.8 34.0 33.2 30.2	27.1 27.3 27.4 27.3 25.7	4.5 4.0 4.0 2.5 2.0	38.8 37.4 36.7 36.9 36.4	30.8 30.7 30.3 30.1 29.3	4.5 3.5 3.0 3.0 3.5
A356-T61	1 2 3 4 5	39.8 37.9 36.5 35.5 33.6	29.4 30.3 29.2 28.5 27.8	6.5 4.5 2.5 2.5 3.0	42.7 42.4 41.6 41.6 41.2	31.6 32.6 31.3 31.6 32.7	10.0 6.5 6.5 6.0 6.0
A357-T62	1 2 3	43.6 41.1 35.5	38.9 38.3 -	1.0 0.5 0.5	47.7 47.2 46.7	40.8 42.1 41.1	3.0 2.5 2.0
A357-T62	1 2 3	33.0 28.1 27.0	31.1 - -	0.5 0.5 0.5	38.8 35.6 35.5	34.0 34.1 33.6	0.5 0.5 0.5

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 at 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	-	39.0 39.0 38.5 38.5 37.5	29.0 29.5 29.0 28.0 29.5	8 8 8 7 7
Control housing	Yes	D5029E	PM, A356-T61	-	43.0 43.0 43.0 42.5 42.0	31.5 31.5 31.5 31.0 31.0	12 15 12 9 9
Fuel Regulator	Yes	D5029F	PM, 356-T6	1,558,000	36.0 35.5 34.5	23.5 23.0 22.0	9 8 6
Fuel Regulator	No	D5028F	PM, 356-T6	355,000	33.5 33.0 32.5	22.0 22.0 23.0	6 6 5
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	-	38.0 38.0 37.5 36.0	22.5 23.5 22.5 21.5	13 16 13 9
Tool plate	Yes	D5029L	PM, 356-T6	3,255,000 1,973,000 1,928,000	35.5 35.0 34.5	24.5 22.5 22.5	6 9 7
Tool plate	No	D5028L	PM, 356-T6	337,000 285,000 285,000	32.0 29.5 27.0	21.5 22.0 23.0	6 3 1.5
Meat slicer	Yes	D5029M	PM, A108-F	341,000	28.0 16.5	13.5 13.0	4 0.0
Meat slicer	No	D5028M	PM, A108-F	83,000	24.5 22.5	15.5 15.0	1.5 1.5
Timing gear cover	Yes	D5029N	PM, 333-T7	-	47.0 45.0 44.0	42.0 41.5 40.5	1.0 1.0 1.0
Timing gear cover	No	D5028N	PM, 333-T7	-	39.5 37.5 36.5	- - -	0.0 0.5 0.0
Timing gear cover	Yes	D5029ON	PM, 333-T7	-	43.5 39.5	41.6 39.0	1.0 1.0
Rocket launcher	Yes	D5029P	SC, A356-T61	2,222,000 1,739,000 1,478,000	42.0 40.0 38.0 38.0	31.0 28.5 31.5 31.0	10 11 3 2.0
Rocket launcher	No	D5028P	SC, A356-T61	584,000 331,000 67,000	37.0 35.5 34.0 27.0	29.5 30.0 28.5 26.5	4 3 3 1.5
Transmission case	Yes	D5029Q	SC, C355-T61	2,254,000 1,957,000	40.0 39.5 39.5	35.5 35.5 34.5	1.5 1.5 3
Transmission case	No	D5028Q	SC, C355-T61	163,000 137,000	33.0 32.5 30.5	32.0 31.5 -	0.5 0.5 0.5
Transmission case	Yes	D5029R	SC, C355-T61	6,307,000 1,101,000	41.0 40.5	36.0 35.0	1.5 1.5
Transmission case	No	D5028R	SC, C355-T61	182,000 108,000	39.5 36.0	33.5 32.5	2.0 0.5
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	34.0 33.0	22.5 22.0	7 6
Carburetor body	No	D5028U	SC, C356-T6	128,000 92,000	29.5	20.5	4
Cylinder	Yes	D5029V	SC, CH70-T7	9,747,000 520,000	71.5 68.5	65.5 63.0	12 11
Cylinder	No	D5028V	SC, CH70-T7	597,000 397,000	71.0 66.0	65.0 60.5	10 6
Piston Part no. 433-177 (head up)	Yes	D5029W	PM, 142-T4	11,241,000 9,452,000	37.0 36.5 35.0 34.5	30.0 30.0 30.0 29.0	0.0 0.0 0.0 0.0
Piston Part no. 433-177 (head up)	No	D5028W	PM, 142-T4	980,000 437,000	34.0 34.0 29.5 29.5	28.5 29.0 28.5 28.5	0.0 0.0 0.0 0.0
Piston Part no. 433-110 (head down)	Yes	D5029X	PM, 142-T4	(2)	36.5 36.5 36.0 36.0	29.0 30.0 29.5 29.5	0.0 0.0 0.0 0.0
Piston Part no. 433-110 (head down)	No	D5028X	PM, 142-T4	226,000	35.5 34.0 33.5 31.0	30.0 29.5 29.5 29.5	0.0 0.0 0.0 0.0
Piston Part no. 433-185 (VRC)	Yes	D5029Y	VRC, 142-T4	22,629,000(3) 20,000,000(3)	41.5 40.5 27.0 37.5	28.5 30.0 (4) 30.0	1.5 1.5 0.0 0.0
Piston Part no. 433-185 (VRC)	No	D5028Y	PM, 142-T4	8,701,000 3,575,000	41.0 40.5 25.5 24.0	30.0 29.5 (4) (4)	1.5 1.5 0.0 0.0

(1) Rotating beam fatigue tests of smooth specimens at 20,000 psi stress.
(2) Specimen broken during machining.
(3) Specimen failed after 20,000,000 cycles but machine did not shut off.
(4) No yield strength reached.

Rotating beam fatigue curves

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