Given safety and performance concerns in the aerospace sector, it may be beneficial to consider quench testing that uses CQI-9 as well as AMS2759 since the automotive standard focuses on safety. Read on to understand the different approaches between these two standards in this Technical Tuesday installment, written by Michelle Bennett, quality assurance senior specialist, and Greg Steiger, senior account manager, both at Idemitsu Lubricants America.
This informative piece was first released in Heat Treat Today’s March 2025 Aerospace Heat Treating print edition.
In today’s world, there are many different quality systems available to heat treaters. Many of these, such as ISO, are quality management systems. These quality management systems are an important piece of running a successful business. However, to successfully run a heat treat business and compete in either the North American automotive market or the aerospace market, a heat treater must conform to either CQI-9 or AMS2759, or, in cases where a company processes both automotive and aerospace parts, both. This article will explain the requirements for both CQI-9 and AMS2759. It will also explain the differences between the two quality standards and any additional testing that could benefit a heat treater or how they operate their quench tank.
AIAG’s CQI-9
The Automotive Industry Action Group (AIAG) is a non-profit group of over 800 automotive OEMS, parts manufacturers, and service providers who oversee the requirements for CQI-9. The 4th edition is the most current edition of CQI-9. As an internal audit process, CQI-9 covers most of the heat treating process. Section 3.14 specifies the quench oil and water-soluble polymer requirements. An oil quenchant requires that the in-use oils be tested every six months and the testing must include water content, percent suspended solids, total acid number, viscosity, flash point, and cooling curve. The specification range and warning limits are based on the vendor’s requirements and recommendations. For water-based polymers, there are two tests required: concentration and quenchability. The standard does not specify a test for quenchability, however, it does make a few suggestions such as a cooling curve, viscosity, and titration.
For water-based polymers, there are two tests required: concentration and quenchability. The standard does not specify a test for quenchability, however, it does make a few suggestions such as a cooling curve, viscosity, and titration.
All the required testing of the quenchant is designed to achieve consistent metallurgy for safety reasons. Viscosity is monitored to look for oxidation or heat decomposition of the oil. Degradation can be in the form of oxidation, thermal breakdown, or the presence of various contaminants. Increased oil viscosity typically results in decreased heat transfer rates. A decrease in viscosity may indicate contamination. Some suspended solids are to be expected during the quenching process, but the majority of them should be filtered or centrifuged from the process. If the quantity of these contaminants becomes too high, then it can both affect the brightness of the parts, and the parts can get soft spots as the contaminants may not cool the parts at the same rate.
Water and flash point are both monitored for safety. If the flash point drops below the accepted range or the water content is above the acceptable range, these can cause fires during the operation. Water can also show issues with the equipment or the procedure such as leaking of anything that is water cooled, such as the outer door on a furnace. Acid value is monitored to degradation of the oil. As the oil breaks down and oxidizes, the acid value will increase. This can cause the maximum cooling rate to increase and can cause cracking or distortion on the parts. Carbon residue can be measured for two reasons. If the result is below the specification, it can show that the quench speed improver is being broken down or dragged out of the system. If the result is higher than the specification, it can show the formation of sludge, which will impact the brightness of the parts.
For water-based quenchants, the most common test items include pH, refractive index or brix, viscosity, and concentration calculation. Sometimes additional test items can be added, such as biological testing, to help determine and correct current issues.
SAE’s AMS2759
Just as AIAG is a non-profit business group responsible for CQI-9, SAE International is a non-profit organization responsible for AMS2759. The most recent revision of AMS2759 is Revision G. AMEC (the Aerospace Materials Engineering Committee) is responsible for maintaining this standard. Unlike CQI-9, AMS2759 requires a certificate of conformance for all shipments. Section 3.10.3 begins the requirements for quenchant testing and quenchant deliveries. Viscosity, flash point, and temperature at the maximum cooling rate must be reported on the certificate of compliance when dealing with mineral oil quenchants. For a polymer, the requirements are that the pH of the neat polymer and the neat viscosity of the polymer must both be reported on the certificate. Also required on the polymer certificate are the viscosity, pH, and the temperature at the maximum cooling rate for polymers at 20% dilution by weight.
Similarly to CQI-9, AMS requires that the in-use quenchants be tested biannually. This standard, however, only requires the cooling rate and temperature at max cooling rate be tested, as well as any additional tests the supplier recommends. The AMS2759 specification does not have set limitations on the cooling rate and temperature. Instead, the specification sets the allowed upper and lower deviations from the supplier’s standard for the maximum cooling rate and the temperature at the maximum cooling rate for both oils and water-soluble polymers. The supplier should have calculated the average max cooling rate and average temperature at max cooling rate using many different blend lots and multiple test runs. This average will not vary or change based on current production values or the values for the batch that the client is currently using (Table 1).
Although both standards require having the quenchant tested bi-yearly, most quenchant suppliers encourage their clients to submit their furnace samples for testing quarterly. This ensures that the medium is being monitored frequently, and if a sample is missed or late when sampling quarterly, then the client is still within compliance for the six month testing requirements.
However, because many of the test parameters in CQI-9 are run for safety reasons along with performance reasons, it is highly advised that aerospace heat treaters should run the full suite of CQI-9 testing along with the AMS2759 testing.
Taking a Quench Sample
There are many different quench methods and both standards allow for any of the following variations: ASTM D6200, ISO 9950, JIS K2242, ASTM D6482, or ASTM D6549. The type of testing that is going to be conducted will determine the size of sample that will be needed. For just this quench testing, the volume of sample needed ranges from 250 milliliters to 2 liters.
As always, when taking samples, it is important to be sure to get a good representative sample of the current quenchant being used in the process. The agitation needs to be running and collected in a clean and dry container. The sampling site should be the most convenient location to safely obtain a sample. It should also be the same location for every sample. The lid also needs to be put on before the oil cools too much because the container will draw in moisture and condensation as the oil cools if it is open to the atmosphere.
Conclusion
When examining the standards, there is one basic commonality: the need to run a complete cooling curve every six months. There is also a large difference in that AMS2759 does not require the full suite of testing that CQI-9 does. However, because many of the test parameters in CQI-9 are run for safety reasons along with performance reasons, it is highly advised that aerospace heat treaters should run the full suite of CQI-9 testing along with the AMS2759 testing. For automotive heat treaters, the maximum cooling rate and the temperature at maximum cooling rate is something that can be reported in the normal D6200 cooling curve test.
For manufacturers heat treating parts for aerospace, automotive, or both markets, we recommend quarterly quench samples at a minimum. The primary reason for more frequent testing is safety. Also, with the current labor shortage, heat treaters are busier than ever. If quench samples are routinely taken on a quarterly basis and are somehow missed and forgotten, there is still time to take another sample and remain in CQI-9 and AMS2759 compliance.
Remaining in compliance of these two important standards requires a lot of hard work from both the heat treater and the quenchant provider. Unless the quenchant supplier is working together in a true partnership, it will be very difficult to remain in compliance with the requirements for CQI-9 and AMS2759. But with routine monitoring, heat treaters can help to ensure quenchant and equipment have a longer life and achieve ever-tightening requirements from clients.
About The Authors:
Quality Assurance Senior Specialist
Idemitsu Lubricants America
Michelle Bennett is the quality assurance senior specialist at Idemitsu Lubricants America, supervising the company’s I-LAS used oil analysis program. Over the past 12 years, she has worked in the quality control lab and the research and development department. Her bachelor’s degree is in Chemistry from Indiana University. Michelle is a recipient of Heat Treat Today’s 40 Under 40 Class of 2023 award.
Senior Account Manager
Idemitsu Lubricants America
Greg Steiger is the senior account manager at Idemitsu Lubricants America. Previous to this position, Steiger served in a variety of technical service, research and development, and sales and marketing roles for Chemtool Incorporated, Witco Chemical Company, Inc., D.A. Stuart Company, and Safety-Kleen, Inc. He obtained a BS in Chemistry from the University of Illinois at Chicago and recently earned a master’s degree in Materials Engineering at Auburn University. He is also a member of ASM International.
For more information: Contact Michelle Bennett at mbennett.8224@idemitsu.com or Greg Steiger at gsteiger.9910@idemitsu.com.
