HIGH CYCLE FATIGUE TESTING
OF "BANADIZED" (AKADIZED) CAST ALLOY (SAE 334)

Background:
A thesis study was conducted by Mr. Hynn-Soo Hong and Dr. Edward Starke at Georgia Institute of Technology during the period of June to December 1982 concerning fatigue failure during "High Cycle Fatigue" testing of Al-Si casting alloys (SAE 334). The study concentrated upon the skirt and pin boss regions of a piston due to the fact that these areas have typically exhibited fatigue problems.

Procedure:
During the Georgia Technology test program, "Banadized" (Akadized) test samples were evaluated to determine the effect, if any, of the coating upon fatigue life. The test specimens were machined from the pin-boss region of a cast alloy (SAE 334) Cummins Engine Co. piston and furnished LTC (Lovatt) in the "T-5" condition to represent a worst case condition for fatigue properties. The specimens were treated with a .0015" to .0020" coating and returned to Dr. Starke for testing at Georgia Tech.
The specimens were subjected to "High Cycle Fatigue" testing and an S-N curve developed based upon the test findings. An S-N curve is defined as a fatigue life curve (stress) versus number of cycles to failure (Nf). The number of cycles to failure decreases with increasing stress. The curve will typically become horizontal at a limiting stress. This limiting stress is known as the fatigue limit. Should no fatigue limit be clearly defined, however, the fatigue limit is defined as the stress amplitude corresponding to a specific number of cycles to fracture (i.e. 107 cycles).
The composition of the test specimens was as follows:

The HCF tests were performed under load control made on an electro hydraulic MTS testing machine with capacities of 10,000 Kg and conducted at 10HZ in sinusoidal fully-reversed tension/compression loading. After 106 cycles, the frequency was changed to 30HZ to decrease the testing time. Testing was discontinued at 107 cycles. A self aligning Wood's metal reservoir was used to insure the coincidence of the machine axis with the specimen axis.

Conclusions:
The Banadized (Akadized) specimens show a significant improvement in the fatigue life of the coated T-5 specimens. This result is a direct contradiction when compared with conventional anodic coatings. A previous study by Cummins Engine Co. stated that anodic coating did not improve the fatigue strength of the alloy SAE 334.
Other published literature has stated that the fatigue strength of aluminum will be degreded from 35 to 60 percent as a result of an anodic coating. An increase in the fatigue strength of the Banadized (Akadized) specimens is therefore very significant indeed! ……. Engineers will not have to accept a degraded fatigue life to use Banadized (Akadized) aluminum.

MICRO-HARDNESS TESTING
OF BANADISED (AKADIZED) ALUMINUM

Background:
A knoop hardness test was run by Eagle-Picker on aluminum samples Banadized (Akadized) at Lovatt in January, 1983. The objective was to compare untreated samples with those that had been Banadized (Akadized). The hardness of any material coating is directly related to the compression abilities of the substrate material. However, the compressive characteristics of the coating itself as well as the interaction between the coating and the substrate (through conversion of the material microstructure) will produce a relative hardness differential between the coated and the uncoated material. Lovatt felt the relative change in the material hardness characteristics could provide a useful piece of information for the applications engineer.

Conclusions:
The study results indicate an increase of the "relative" material hardness for Type 6061 Aluminum Alloy of 367 to 505 percent with the Banadized (Akadized) coating.
The study also indicates an increase of 201 percent for the "relative" material hardness of Type 7075 Aluminum Alloy with the Banadized (Akadized) coating.
A determination was not made for the "relative" change of the SXA (Metal Matrix Composite) specimens. The only uncoated sample available for the test was too warped to make a good hardness determination.

SALT SPRAY CORROSION TESTING
OF ANODICALLY COATED "BANADIZED" (AKADIZED)
ALUMINUM

Salt Spray Corrosion Tests have been run on various aluminum alloys treated with a "banadized" (akadized) coating. Testing conformed to the requirements of
Mil-A-8625C and ASTM B117. The following table is a summation of those tests:

Static and Kinetic Coefficients of Friction
For "Banadized" (Akadized) Aluminum

Background:
The purpose of these tests was to measure the coefficient of friction of the submitted materials utilizing the procedure advocated in ASTM D 1894-Standard Test Method for Static and Kinetic Coefficient of Friction of Plastics Film and Sheeting.

Procedure:
The coefficient of friction was measured by pulling the 2" x 4" panel (rider) horizontally with a known additional load over the larger panel (base plate). The force required to start motion and the force required to move the rider at a uniform speed where recorded with a calibrated load cell. These forces were measured while pulling the rider at two speeds and with two different weights on the rider at each speed. The coefficient of friction was calculated by the following relations:

Conclusions:
The Banadized (Akadized) coating produced a decrease in the frictional coefficients of 28 to 33 1/3% for the type 7075 alloy material.

Taber Abrasion Testing
Of "Banadized" (Akadized) Aluminum

Background:
Taber Abrasion tests have been conducted on Banadized (Akadized) aluminum specimens in accordance with Mil-A-8625C, Amendment 1. The test utilized a Taber Abrasion Tester Model 503 (or equivalent). The test specimens were 4" x 4" x .32" thick "Banadized" with a .002" thick treatment.
Two tests were conducted on the subject materials. The first test was the Standard Mil-A-8625C test which consisted of measuring the milligram weight loss after 10,000 cycles using a 1000 gm load and CS-17 abrasion wheels.
The second abrasion test consisted of a "total" abrasion test where the coating was abraded until the base metal was reached. The 1000 gm load and the CS-17 abrasion wheels were also used for this test.

Conclusions:
It can be readily be seen from the Mil-A-8625C test table that all of the Banadized samples surpassed the Mil Std. Requirement losing considerably less than 20 mg. During the 10,000 cycles. Also a review of the "Total Abrasion" test table indicates that the coating will surpass the Mil-A requirement by 7 to 10 times the specified coating life.

Thermal Conductivity/Emmissivity
Testing of Banadized (Akadized) Aluminum

Background:
The following tests have been run using "Banadized" treated aluminum alloys. The testing covered a "Thermal Conductivity" determination as well as an "Emissivity" evaluation.

Results:
I. Thermal Conductivity

II. Emissivity

Optical and Microwave Measurements
of "Banadized" (Akadized) Aluminum

Background:
A series of "Optical" and "Microwave" tests were run on various aluminum alloys Banadized by Lovatt Technology. This report presents the results of that testing. The testing was done by the Naval Weapons Center at China Lake, California.

All samples were in the form of a 7.0mm diameter cylinder with a 3.04mm central hole, and were approximately 4mm in thickness. These samples formed a snug fit in a 7mm precision coaxial air line. The measurements were taken on a computer-controlled Hewlett-Packard 8410 automatic network analyzer; this analyzer measured the value of Sii of the S-parameter matrix, a quantity known as the return loss, from which the reflection coefficient can be computed. Data was taken over the frequency range of 2.0 to 18.0 GHz in steps of 0.5 GHz. The measurements were made first of the reflection coefficient of the treated side of the donut-shaped sample; the sample then was reversed and measurements were taken of the untreated side. This technique allowed variations in the reflection coefficient that arise from unavoidable differences in sample size due to machining tolerances to be identified.

Conclusions:
These results indicate that within the accuracy of the automatic network analyzer the treated surface cannot be distinguished from the bare aluminum surface. The treatment has no measurable effect on the reflection coefficient of electromagnetic waves in the frequency range from 2.0 to 18.0 GHz. The difference in reflection coefficient between the silver-plated copper reference short and the aluminum samples is due to the lower bulk conductivity of aluminum.
All of the samples displayed a very low reflectance both in the visible and infrared spectral regions, but a high reflectance (essentially identical to that of aluminum) in the microwave region. The scattering levels were quite high in the visible and lower in the infrared.
The scattering levels are high enough that the expression obtained from scaler scattering theory that is normally used to calculate a value of surface roughness is not valid, therefore, the roughness values in the 400-600 Angstrom region reported are probably incorrect.
The most striking thing about the optical measurements is the very large absorption of the coated samples both in the visible and infrared.

Specular Reflectance of Banadized (Akadized) Aluminum

Background:
The "Infra-Red Reflectivity" was measured using "Banadized" aluminum specimens. A Perkin-Elmer 283 Ratio Reading Spectrophotometer was used to measure the specular reflectance of the samples. An aluminum mirror was used as a reference sample.

Conclusions:
All of the coated samples displayed a very low reflectance both in the visible and infrared spectral regions. The graphs are self-explanatory and may be of benefit to the applications engineer in the form presented. These test results, run at Eagle-Picher's Miami Research Labs in Miami, Oklahoma duplicate the results of similar investigations by both Hughes Aircraft and the Naval Weapons Center at China Lake, California.