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by | May 26, 2024

Key Takeaways:

  • Enhanced Corrosion Resistance: AMS-QQ-P-35 ensures stainless steel components receive a thorough passivation treatment, enhancing their resistance to corrosion in aerospace, defense, and space applications, crucial for prolonged durability and safety. 
  • Standardized Process for Reliability: Adhering to AMS-QQ-P-35 provides manufacturers with a standardized and well-documented approach to passivation, ensuring consistency and reliability in component performance across various industries, including aerospace and medical devices. 
  • Optimized Quality Control: Implementing rigorous quality control measures, including visual inspections and chemical spot tests, ensures the effectiveness of the passivation process under AMS-QQ-P-35 standards, maintaining high-quality standards and compliance with industry requirements.


The aerospace industry demands materials that can withstand the harshest environments. Stainless steel, a popular choice for its strength and versatility, requires additional treatments to optimize its performance in these demanding conditions.

For decades, AMS-QQ-P-35 served as the established aerospace material specification by SAE International, outlining a comprehensive approach to achieving optimal corrosion resistance in various stainless steel components.

In this article, we will discuss the key aspects of the AMS-QQ-P-35 specification, including its importance, the processes involved, and the benefits it provides to corrosion-resistant steel applications.

At Valence Surface Technologies, we understand the criticality of adhering to such standards, reinforcing our commitment as a trusted leader in aerospace surface finishing. Our extensive capabilities and innovative solutions make us the preferred choice for companies needing top-of-the-line surface treatment that strictly complies with AMS-QQ-P-35 requirements. 


What Is AMS-QQ-P-35?

AMS-QQ-P-35 is a specification set by the Society of Automotive Engineers (SAE) for the passivation of corrosion-resistant (stainless) steel parts. This standard outlines the requirements and procedures for the passivation process, which involves removing contaminants from the surface of stainless steel to enhance its corrosion resistance and improve its longevity and performance.

The protocol specified various types of acids and treatments that could be used for passivation, tailored to different grades of stainless steel and desired outcomes. This specification ensured that parts treated under its guidelines met rigorous performance standards, crucial in applications where failure could have catastrophic consequences.


The Science Behind AMS-QQ-P-35

The science behind AMS-QQ-P-35 revolves around the process of passivation, which is aimed at enhancing the corrosion resistance of stainless steel components. Passivation involves the removal of free iron and other surface contaminants from stainless steel to promote the formation of a passive oxide layer.

This passive oxide layer gives stainless steel its corrosion-resistant properties. The passivation process typically involves immersing the stainless steel parts in an acidic solution, such as nitric or citric acid, under controlled conditions of temperature, time, and concentration.

During passivation, the acid removes impurities and contaminants from the surface of the stainless steel, including any free iron particles that may be present from machining or handling. This cleaning process promotes the formation of a uniform and stable oxide layer on the steel’s surface.

The passive oxide layer acts as a protective barrier, preventing further corrosion and oxidation of the underlying metal. It effectively seals the surface of the stainless steel, making it more resistant to rust, staining, and other forms of corrosion in harsh environments.


Benefits Of Using AMS-QQ-P-35 In Manufacturing

Here are some of the key benefits of using AMS-QQ-P-35 in manufacturing, particularly for aerospace applications:


Enhanced Corrosion Resistance

The primary benefit lies in significantly improving corrosion resistance for stainless steel components. The passivation process, outlined in AMS-QQ-P-35, creates a thicker and more robust chromium oxide layer that acts as a barrier against various corrosive elements. This is crucial for aerospace parts exposed to harsh environments with moisture, extreme temperatures, and high altitudes.


Improved Component Performance and Longevity

By minimizing corrosion, AMS-QQ-P-35 passivation helps ensure stainless steel components’ long-term performance and reliability. This translates to reduced maintenance costs and safer operation of aerospace vehicles.


Material Versatility

AMS-QQ-P-35 applies to a wide range of stainless steel types, including austenitic, ferritic, martensitic, and precipitation hardening grades. This allows manufacturers to leverage the benefits of passivation across various applications within an aerospace project.


Standardized Process

While superseded, AMS-QQ-P-35 provides a well-defined and documented approach to passivation. This ensures consistency and repeatability in the treatment process, resulting in reliable component performance.


Industry Recognition (indirect benefit)

Adherence to AMS-QQ-P-35 demonstrates a commitment to quality and adherence to established practices within the aerospace industry. This can be valuable for manufacturers seeking to qualify for specific projects or contracts.


Detailed Passivation Processes In AMS-QQ-P-35

AMS-QQ-P-35, a critical specification within the aerospace industry, provides standardized guidelines for the passivation of stainless steel components. This process enhances the material’s corrosion resistance, which is crucial for parts exposed to harsh operational environments typical in aerospace, defense, and space applications.

The Passivation Treatment

Passivation involves treating stainless steel with a mild oxidant to remove free iron from the surface and promote the formation of a thin, transparent oxide film that acts as a barrier, protecting the metal from corrosion. In accordance with AMS-QQ-P-35, several types of passivation treatments are specified, each tailored to different stainless steel grades and conditions.

Types of Passivation Solutions

  • Nitric Acid Solutions: This is the most commonly used passivation solution, effective for various stainless steel compositions. It typically contains 20-50% nitric acid by volume and is maintained at 120 to 140°F. The treatment duration varies from 20 minutes to two hours, depending on the stainless steel type and the desired corrosion resistance. 
  • Citric Acid Solutions: Citric acid is an environmentally friendly alternative to nitric acid. It promotes the formation of a passivation layer without discharging high levels of dangerous fumes. This solution generally comprises 4-10% citric acid by weight and is used at temperatures ranging from 70 to 160°F.


Handling and Rinse Procedures

Post-treatment handling and rinsing are crucial to ensuring the effectiveness of the passivation process. AMS-QQ-P-35 specifies that parts should be thoroughly rinsed with water immediately after removal from the passivating solution to remove any residual acids that might compromise the integrity of the passivation layer. A final drying step, often employing hot air or vacuum drying techniques, is also recommended to prevent water spots which could result in localized corrosion.


Inspection and Testing

Passivated stainless steel parts undergo inspection and testing to verify the effectiveness of the passivation process. This may include visual inspection for surface cleanliness and uniformity and various corrosion tests to assess the durability and performance of the passivated parts.


Industry Applications Of AMS-QQ-P-35

AMS-QQ-P-35 finds widespread application across various industries where corrosion-resistant stainless steel components are essential. Here are some key industry applications of AMS-QQ-P-35:


Aerospace and Aviation

In aerospace and aviation, the integrity of component surfaces is non-negotiable. The passivation processes outlined in AMS-QQ-P-35 help enhance the corrosion resistance of parts constantly exposed to high humidity, temperature fluctuations, and corrosive environments. This treatment ensures that aerospace components can withstand the rigors of operation while maintaining safety and longevity.


 Aerospace and Aviation



The defense industry requires materials that can endure extreme conditions and rigorous use. Passivation treatments as per AMS-QQ-P-35 standards are critical in preventing rust and corrosion on military vehicles, weaponry, and other equipment. This not only prolongs the life of the materials but also enhances their reliability in critical situations.


Space Industry

Equipment reliability and structural integrity are of the utmost importance in space exploration. The harsh conditions of outer space, including exposure to vacuum, radiation, and extreme temperatures, demand that every component be treated to resist corrosion effectively. AMS-QQ-P-35 passivation processes ensure that metal parts used in spacecraft and satellites achieve and maintain the necessary resilience.

Medical Devices

AMS-QQ-P-35 is vital for passivating stainless steel parts used in medical devices and equipment, including surgical instruments, implants, and diagnostic tools. Passivation ensures these critical medical components’ biocompatibility, corrosion resistance, and cleanliness.


Common Challenges And Solutions In AMS-QQ-P-35 Passivation

While AMS-QQ-P-35 passivation offers significant benefits, several challenges may arise. Here are some common challenges and their corresponding solutions:


Contaminant Removal

  • Contaminants such as oils, greases, and surface oxides can hinder passivation.
  • Solution: Thorough pre-cleaning using appropriate solvents or alkaline cleaners ensures effective removal of contaminants before passivation.


Uniformity of Passivation

  • Achieving uniform passivation across complex or large stainless steel parts can be challenging.
  • Solution: Implementing agitation or circulation systems in passivation baths helps ensure uniform exposure of all surfaces to the passivating solution.


Handling of Hazardous Chemicals

  • Nitric acid, commonly used in passivation, poses safety and environmental risks.
  • Solution: Implementing proper safety protocols, personal protective equipment (PPE), and appropriate ventilation systems minimizes risks associated with handling hazardous chemicals.


Post-Passivation Rusting (Flash Rust)

  • Stainless steel parts may develop flash rust if not adequately dried after passivation.
  • Solution: Implementing thorough drying processes, such as hot air or vacuum drying, ensures complete moisture removal and prevents flash rusting.


Quality Control and Testing

  • Ensuring the effectiveness of the passivation process through comprehensive testing can be time-consuming.
  • Solution: Implementing automated testing procedures, such as salt spray or copper sulfate tests, streamlines quality control and ensures consistent passivation results.


Environmental Compliance

  • Disposal of passivation chemicals and rinse water must comply with environmental regulations.
  • Solution: Implementing proper waste management practices, including neutralization and adequate disposal of chemicals, ensures compliance with environmental regulations.


Compatibility with Complex Parts:

  • Passivating intricate or highly stressed components may require customized solutions.
  • Solution: Employing specialized techniques, such as brush or spray passivation, allows for effectively treating complex parts while maintaining passivation quality.


Process Validation

  • Ensuring that the passivation process meets AMS-QQ-P-35 requirements and customer specifications.
  • Solution: Implementing regular process validation measures, such as audits and documentation reviews, ensures compliance with standards and customer requirements.


Comparing AMS-QQ-P-35 With Other Passivation Standards

Comparing AMS-QQ-P-35 with other passivation standards is imperative to ensure the highest quality and consistency in aerospace, defense, and space applications. Here’s a breakdown of some key comparisons:


AMS-QQ-P-35 and ASTM A967

ASTM A967 is another popular passivation standard. While AMS-QQ-P-35 specifically targets stainless steel components used in the aerospace industry, ASTM A967 offers a more flexible approach that can be applied to various industries. AMS-QQ-P-35 typically requires more stringent passivation solutions, such as sodium dichromate, reflecting its aerospace-focused performance requirements.


AMS-QQ-P-35 and ASTM A380

ASTM A380 is focused on cleaning, descaling, and passivating stainless steel parts. Unlike AMS-QQ-P-35, it provides comprehensive guidelines that include not only passivation but also pre-treatment processes.

The specificity of AMS-QQ-P-35 in the types of stainless steel and the required cleanliness levels before passivation make it more tailored for aerospace components, where utmost precision and reliability are needed.


Quality Control Testing Requirements Within AMS-QQ-P-35

This information can be useful for understanding the evolution of passivation best practices and interpreting legacy components potentially treated according to AMS-QQ-P-35.


Ensuring Passivation Effectiveness

Implementing rigorous QC testing procedures ensures the passivation process has been successful and that the components meet the industry’s stringent performance standards.


Potential Testing Methods

  • Visual Examination: Meticulously inspect the passivated components to identify any surface defects, inconsistencies, or discoloration. 
  • Surface Roughness Measurement: Measuring the surface roughness before and after passivation can indicate the cleaning process’ effectiveness and potential impact on the passivation layer’s uniformity. 
  • Chemical Spot Tests: These tests utilize specific solutions to assess the presence and quality of the chromium oxide layer formed during passivation. 
  • Weight Loss Testing: This method involves measuring the weight loss of a sample before and after a controlled corrosion test, providing insights into the effectiveness of the passivation treatment.


Sampling and Documentation

AMS-QQ-P-35 likely specified sampling procedures for selecting representative test specimens from each batch of passivated components. Maintaining meticulous documentation of the testing process, results, and non-conforming components would have been crucial for upholding quality control records.


Critical Considerations For Using AMS-QQ-P-35

When implementing AMS-QQ-P-35 standards in aerospace product finishing, several key considerations must be observed to ensure optimal outcomes:


Material Compatibility

The selection of suitable materials compatible with AMS-QQ-P-35 is crucial. Different materials react differently to the passivation process. Understanding the specific characteristics and needs of materials such as stainless steel variants is essential to avoid potential damage and ensure the integrity of the component.


Process Parameters

Adhering to the specified process parameters defined by AMS-QQ-P-35 is vital for achieving desired results. This includes controlling temperature, time durations, and chemical concentrations during the passivation process. Precise control helps achieve a uniform and defect-free passivation layer, which is essential for enhancing corrosion resistance.


Environmental Considerations

Environmental factors play a significant role in the passivation process. Factors such as humidity and contamination in the working area can affect its efficacy. Ensuring a clean and controlled environment is imperative to prevent process interruptions and potential rework, which can increase production costs.


Quality Control

Implementing stringent quality control measures is essential when working under the AMS-QQ-P-35 standards. Regular testing and monitoring throughout the passivation process help identify issues early, ensuring that the final product meets the high-quality standards required in the aerospace sector. This involves visual inspections and more detailed analyses, such as ferroxyl testing, to detect surface-free iron contamination.


Compliance and Documentation

Maintaining comprehensive documentation and ensuring full compliance with AMS-QQ-P-35 guidelines and other applicable regulations is critical. This facilitates smoother certification and quality audits and enhances the traceability and reliability of the finished products.


Compliance and Documentation


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Frequently Asked Questions

What types of stainless steel are covered under AMS-QQ-P-35?

AMS-QQ-P-35 covers a variety of stainless steel types, including, but not limited to, 300 series, 400 series, and precipitation-hardening stainless steels. The specification provides guidelines for passivating these metals to enhance their corrosion resistance.


What are the different treatments specified in AMS-QQ-P-35?

AMS-QQ-P-35 specifies different passivation treatments based on the stainless steel composition and desired outcomes. These treatments typically involve cleaning the metal surface followed by the application of an acid solution, such as nitric or citric acid, to remove free iron and other contaminants, thereby enhancing the stainless steel’s natural corrosion resistance.


What documentation is required for AMS-QQ-P-35 compliance?

Documentation for AMS-QQ-P-35 compliance typically includes process validation records, certificates of compliance, and detailed process specifications. These documents ensure that all treatments meet the stringent requirements outlined in the specification and that the passivation process is consistently effective.


How often should parts be passivated according to AMS-QQ-P-35?

According to AMS-QQ-P-35, the frequency of passivation depends on factors such as the part’s usage, environment, and application-specific requirements. However, it is generally recommended to re-passivate stainless steel parts periodically or after any operations that could compromise the integrity of the passive layer, such as welding or machining.


Is AMS-QQ-P-35 recognized internationally?

Yes, AMS-QQ-P-35 is recognized internationally as a standard practice in aerospace and other industries for passivating stainless steel parts. It aligns with global industry standards and is often referenced in international specifications and contracts.


Can AMS-QQ-P-35 passivation be done in-house?

While AMS-QQ-P-35 passivation can technically be done in-house, it requires specific equipment, trained personnel, and a controlled environment to meet stringent quality and safety standards. 


What are the typical costs associated with AMS-QQ-P-35 passivation?

The costs associated with AMS-QQ-P-35 passivation can vary depending on the size and complexity of the parts, the type of stainless steel, and the specific requirements of the passivation process. Outsourcing to a specialist like Valence Surface Technologies can often be cost-effective, considering the expertise and equipment required.


How can I ensure my parts meet AMS-QQ-P-35 requirements?

Ensuring that your parts meet AMS-QQ-P-35 requirements involves selecting a reputable and experienced service provider with a proven track record of compliance. Service providers should clearly understand AMS-QQ-P-35 specifications, state-of-the-art equipment, and a detailed process control system.


Is AMS-QQ-P-35 related to other aerospace specifications?

Yes, AMS-QQ-P-35 is related to other aerospace specifications, particularly those concerning metal components’ fabrication, treatment, and finishing. It often works hand-in-hand with other specifications to ensure aerospace parts’ overall quality and performance.


Are there alternatives to AMS-QQ-P-35 passivation?

Alternatives to AMS-QQ-P-35 passivation exist, including newer methods and technologies that might offer different benefits, such as enhanced corrosion resistance or reduced environmental impact. It is important to consult with specialists like Valence Surface Technologies to understand the best options for your specific application needs.

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