Ultrasonic Cleaning for Metals: Best Practices for Brass, Copper, Stainless Steel & More

Ultrasonic cleaning detergents come in several varieties.

Alkaline detergents are generally the most effective for cleaning metal parts. These high-pH cleaning solutions break down oils, greases, particulates, and even rust or scale, depending on their strength. While other detergent types – such as acidic or enzymatic cleaners – may be appropriate for specific applications, this article focuses on best practices for using alkaline detergents to clean common metals.

There are two main types of alkaline detergent:

• Standard alkaline detergent – used for sensitive metals such as copper, brass, or aluminum. This formulation is designed to lift oils and light soils without risking discoloration or etching. UPC has created Sonic Power Degreaser as a standard alkaline detergent.
• Heavy-duty alkaline detergeant – used for tougher jobs, such as removing rust, scale, or baked-on contaminants. These solutions are typically high in pH and are especially effective on ferrous metals like carbon steel and stainless steel. UPC has created Sonic Power HD as a heavy-duty alkaline detergent.

Read more about choosing a detergent for your ultrasonic cleaner

This guide provides material-specific ultrasonic cleaning recommendations, including detergent compatibility and operating precautions.

Always test sensitive or reactive metals before full-scale cleaning.

Good quality ultrasonic cleaners are highly configurable, so they can be adjusted to deliver optimum performance for a wide range of materials and applications.

Key configuration parameters include:

• Temperature of the cleaning solution 

Cleaning solution temperature has a significant impact on performance. Too low and the cleaning process may not be effective. Too high and reactive metals may be damaged.

• Cleaning time 

The cleaning time depends on the application. Too short a time may not deliver optimum results. However, reactive materials can suffer from cavitation erosion if they’re exposed to ultrasonic cleaning for too long. 

• Frequency of the ultrasound waves

Lower frequency waves (25–40 kHz) produce more intense cavitation bubbles, while higher frequencies (68–170 kHz) offer gentler cleaning action, which may be required for reactive metals.

Read more about the factors affecting the ultrasonic cleaning process

Ultrasonic Cleaning for Stainless Steel

Stainless steel is highly compatible with ultrasonic cleaning. Most common grades – like 304, 316L, and 17-4 PH – can be safely cleaned with either a standard or heavy-duty alkaline detergent.

• Use a heavy-duty detergent for removing rust, scale, heavy oils, or burned-on debris
• Cleaning temperatures can go as high as 175°F
• Always follow with thorough rinsing to avoid water spots or detergent residues

Stainless steel is non-reactive and is safe to clean alongside other non-reactive metals. It shouldn’t be mixed with copper or brass.

Ultrasonic Cleaning for Brass and Copper

Brass and copper are considered reactive metals. They require milder detergents and careful isolation from other parts.

• Use a standard alkaline detergent (never a heavy-duty detergent)
• Keep the bath temperature under 140°F
• Clean in separate containers or baths to prevent copper redeposition on other metals

Copper particles can linger in the bath and ‘plate’ onto stainless steel or titanium, leading to contamination and staining.

Ultrasonic Cleaning for Aluminum and Magnesium

Aluminum and magnesium alloys are highly sensitive to ultrasonic cleaning, especially at lower frequencies (like 40 kHz). Risks include cavitation erosion, surface pitting, and discoloration at high temperatures.

• Use a standard alkaline detergent (never a heavy-duty detergent)
• Keep the bath temperature under 140°F to prevent darkening and erosion
• Avoid lower ultrasonic frequencies
• Limit cycle times to prevent surface etching or discoloration

Always test sensitive metals before full-scale cleaning.

Ultrasonic Cleaning for Exotic Alloys (Titanium, Inconel, Haynes, etc.)

Titanium is generally compatible with ultrasonic cleaning. Other exotic alloys – such as Inconel, Haynes, cobalt-chrome, and Hastelloy – can be cleaned with ultrasonics but require extra caution.

• Titanium alloys like Ti-6Al-4V can tolerate heavy duty detergents but only for short cycles (typically under 10 minutes)
• Inconel, Haynes, and cobalt-chrome alloys should only be used with a standard alkaline detergent andshould be cleaned at lower temperatures
• Always test exotic alloys before full-scale cleaning or contact the manufacturer for advice

Ultrasonic Cleaning for Mixed Metal Loads

Some combinations of metal types should be avoided in ultrasonic cleaners.

• Copper residue can ‘plate’ onto other metals
• Reactive metals can contaminate the bath, leading to poor results

To avoid these issues:

• Use dedicated cleaning cycles for reactive and non-reactive metals
• Use nested containers (also known as ‘bread pans’) for isolated cleaning within the same tank
• Change the cleaning solution regularly to prevent buildup of particles and residues

Ultrasonic Cleaning: Part Fixturing and Orientation

For best results, parts should be positioned in a way that maximizes exposure to ultrasonic waves.

Avoid allowing surfaces to rest directly on the tank floor or against other parts. Use baskets or fixtures that allow full immersion and ensure all critical surfaces are exposed. Good fixturing also improves rinsing and drying by preventing trapped air pockets or residual water.

Ultrasonic Cleaning: Rinsing and Drying

Following ultrasonic cleaning, most objects need to be rinsed to remove traces of detergent or solvent and any loosened contaminants on the items. Parts should be dried as soon as rinsing is complete to prevent water spots or corrosion.

• Rinsing can be done by immersing or spraying items in a separate tank using clean or deionized (DI) For extra thorough rinsing, further rinsing cycles can be included in the process.
• Using ultrasonics in the rinsing process is the most effective and efficient way to ensure that items are free from microscopic contaminants and residues.
• Parts can be air dried by blow drying with compressed air or by placing the parts in a drying cabinet. Sensitive items may need controlled temperature or vacuum drying.

Final Note

Ultrasonic cleaning delivers reliable and high quality results for many different metals – but it’s important to follow the rules. These include knowing which metals require care, which detergents to use, and which metals you can clean together. With care, you can extend part life, ensure safety, and achieve optimum cleaning results.

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