Guide
Can MIM Parts Be Plated or Passivated Like Wrought Stainless?
MIM parts are dense metal components, with interconnected porosity that MIMA says is typically below 0.2%, so plating and coloring need no special preparation, unlike press-and-sinter parts. Passivation of MIM stainless is the open point: the sources do not address it, so it is proven on a trial lot.
By Saola Manufacturing engineering team · Published · Updated
On this page
Can MIM parts take standard plating and coloring?
Yes, on the evidence of the industry association. MIMA states that MIM typically limits a part’s interconnected porosity to less than 0.2%, and that standard coloring and plating techniques can be applied without special surface preparation.
That sentence is the whole basis for treating a MIM part like a wrought one at the plating line, and it is worth reading for what it does not say. It is about plating and coloring. The MIMA list of surface treatments names polishing, coating, painting, cleaning, anodizing and plating, among others, and it does not mention passivation (MIMA, Secondary Operations with MIM). A second independent source agrees on the plating point: a general encyclopedia entry says the MIM component is compatible with metal conditioning treatments such as plating (Metal injection molding).
This guide is for an engineer or buyer who needs a finish on a MIM stainless or steel part: nickel, chrome, another plated layer, or passivation. It explains why MIM differs from press-and-sinter powder metal, what remains unproven for passivation, and what to put on the drawing. It gives no coating thickness, no corrosion-test hours and no prices, because none of the sources behind it publishes them for MIM.
What is different about press-and-sinter parts?
Press-and-sinter parts are less dense, and their interconnected pores can reach the surface, so a finish on them may need sealing or resin impregnation first. PickPM notes that porosity in PM parts significantly affects corrosion resistance and that higher density improves it.
PickPM describes porosity in PM parts as possibly a network of interconnected pores that extend to the surface like a sponge. Its secondary-operations page lists plating, steam treating, infiltration and resin impregnation, and says resin impregnation can be done to prepare the surface for plating, while steam treating and infiltration seal porosity. The contrast is the guidance. For a dense MIM part, the sources describe no special preparation. For a press-and-sinter part, they describe options that exist because the pores are a problem.
Why open pores matter to a finish is a point of engineering reasoning, not a figure from the sources: pores that reach the surface can hold process solutions and let them bleed back out after the finish is on. That is why the sealing step exists, and it is the reason to ask which kind of powder metal part you are buying before you accept a finish note written for another.
| Topic | Metal injection molding | Press-and-sinter powder metal | Source |
|---|---|---|---|
| Density | Typically 96% to 99% of theoretical in a controlled atmosphere | Structural parts have relative densities from 80% to above 95% | MIMA Process Overview; PickPM Engineering Properties |
| Interconnected porosity | Typically limited to less than 0.2% | Pores can form a network extending to the surface like a sponge | MIMA Secondary Operations; PickPM |
| Preparation for plating | None special for standard coloring and plating | Resin impregnation can be used to prepare the surface for plating | MIMA; PickPM Secondary Operations |
| Sealing options | Not described as needed | Steam treating, infiltration or resin impregnation to seal porosity | PickPM Secondary Operations |
| Corrosion resistance | Not quantified in these sources; ask for test evidence | Porosity significantly affects it, and higher density improves it | PickPM Engineering Properties |
Can MIM stainless be passivated like wrought stainless?
The sources behind this guide do not say, so treat it as something to prove on a trial lot with the acceptance tests in ASTM A967. The MIMA surface-treatment list does not mention passivation, and the standards do not address sintered parts.
ASTM A967/A967M-25 covers chemical passivation of stainless steel parts by nitric acid immersion, citric acid immersion and electrochemical treatment. It makes no recommendation on which grade, treatment or acceptance criteria suit a particular application, and it lists qualitative acceptance tests: water immersion, high humidity, salt spray, copper sulfate, and potassium ferricyanide with nitric acid, with a separate free iron test. Passed parts should show no etching, pitting or frosting on visual inspection. ASTM A380/A380M-25 is the companion practice for cleaning, descaling and passivating stainless steel parts, equipment and systems.
Neither standard says that sintered parts are included or excluded, and the sources behind this guide do not either. So the sensible route is a trial: name the standard and the treatment on the drawing, pick one acceptance test from the standard, and run it on a sample lot of your MIM part before you commit the order. The wrought-part view is in the guides on passivation of machined stainless parts and electropolishing versus passivation, and the vocabulary carries over.
What should the drawing and RFQ say about the finish?
Name the finish standard and class, the faces and the masked areas, whether the finish goes on before or after machining, the acceptance test, and the fact that the part is MIM. Then ask for the supplier’s statement on the porosity of the grade.
- The finish specification, class and thickness callout, tied to a standard you hold.
- The faces that take the finish, and the threads, bores and datum faces that are masked or left bare. The guide on threads after anodizing and plating covers the thread side.
- The order of operations: finish before or after the CNC step that adds threads or tight faces.
- The acceptance test and sampling, for example one of the ASTM A967 tests for passivation, with the pass criterion written down.
- The statement that the part is metal injection molded, and the density or interconnected porosity the supplier expects for the grade.
- A trial lot or first-article sample with the finish applied, before volume is released.
For the plating side, the guide on plating defects lists what to look for in incoming parts. It is written for machined parts, so add one MIM-specific check: look for staining that appears after the finish has been on for a while, because that points to bleed from open pores.
What failures point to porosity, and what then?
Staining that appears after plating or passivation, blisters, and a part that passes the first test but fails after storage all point to pores holding solution. Stop the lot, ask the processor what was done, and ask whether sealing or a different cleaning route applies.
These are field symptoms read through the engineering logic above, not statements from the sources, so treat them as prompts for a conversation. The fix may be a different rinse and dry route, a different sealing step, or a change of the part from press-and-sinter to MIM where density allows. Whatever the route, ask for the same acceptance test to be repeated on the corrected lot and keep the written result.
If the part is a dense MIM grade and the failure still occurs, the cause is probably not the porosity the sources describe. Look at the cleaning before plating, the condition of the surface from the furnace, and the bath. The guide on plating defects covers those, and the supplier’s process record should show them.
How does a managed program handle MIM and the finish?
Saola places MIM work and surface finishing through partner plants it manages, and neither is described as a Saola process. The quote states the production site and the country of origin, and faces and threads that need machined tolerances are finished by CNC.
The MIM and powder metal capability page and the surface finishing page describe how the two are organized. Ask in the RFQ which plant runs the finish, so that the sequence of sintering, machining and finishing is a stated plan, and send the drawing with the finish note and the acceptance test already written.
Frequently asked
Does MIM stainless need sealing before plating?
MIMA says standard coloring and plating techniques can be applied without special surface preparation, because interconnected porosity is typically limited to less than 0.2% (MIMA, Secondary Operations). Confirm it for your grade and finish with a trial lot.
Why do press-and-sinter parts need different handling?
Their porosity can be an interconnected network reaching the surface, and PickPM lists resin impregnation, steam treating and infiltration as ways to prepare for plating or to seal (PickPM, Secondary Operations).
Is passivation the same as plating?
No. Plating adds a metal layer. Passivation is a chemical treatment of stainless steel, covered in ASTM A967/A967M-25, that removes free iron and helps form the passive film.
Is a MIM part as corrosion resistant as a wrought part?
The sources do not quantify it. MIMA says MIM properties are similar to annealed conventional metal and PickPM says higher density improves corrosion resistance, so ask the supplier for test evidence in your environment.
Which platings can powder metal take?
PickPM lists plating with copper, nickel, zinc and chromium, among others, for ferrous powder metal parts, with corrosion resistance and appearance as the objectives (PickPM).
Sources
- MIMA, Secondary Operations with MIM, Metal Injection Molding Association, accessed October 2026
- MIMA, Process Overview: MIM, Metal Injection Molding Association, accessed October 2026
- PickPM, Engineering Properties, PickPM design center, accessed October 2026
- PickPM, Secondary Operations, PickPM design center, accessed October 2026
- ASTM A967/A967M-25, Standard Specification for Chemical Passivation Treatments for Stainless Steel Parts, ASTM International store page, last updated January 2025
- ASTM A380/A380M-25, Standard Practice for Cleaning, Descaling, and Passivation of Stainless Steel Parts, Equipment, and Systems, ASTM International store page, last updated January 2025
- Metal injection molding, Wikipedia, accessed October 2026