Corrosion tests II: Most common types of tests

Imagen para enseyosde corrosión INELCA SLU

In the previous instalment of this publication we saw the definition, purpose and limitations of corrosion tests, in this instalment we will discuss the most widespread types of corrosion tests used to test metal parts coated with sacrificial metals such as Zn, ZnFe, ZnNi and Zn flakes.

CNS test:

The initials of this test correspond to the Salt Fog Chamber, currently it is perhaps the most extensive test to evaluate the quality of coatings deposited on steel parts. It consists of introducing the pieces to be tested in a chamber that is filled with mist by means of a nebulizer formed from a solution of distilled water with 5% NaCl (salt), with humidity, temperature and pH of the chamber under standardized parameters. The permanence within the CNS will depend on the type of coating to be tested and the specification established by the end user of the parts. During the test, which can go from 24 h to 3000 h or more, the condition of the samples is evaluated every 24 h, and both the corrosion of the coating (CB: white corrosion) which will appear first, and the corrosion of the steel ( CR: Red Corrosion)

Climatic tests:

As we discussed in the previous instalment, corrosion tests cannot be correlated with the useful life of the piece-coating assembly, in order to bring the time of use and test relationship closer several years ago the automotive sector began to specify climatic tests on treated parts. For this, each manufacturer defined a unique test cycle tailored to their needs, thus creating another type of corrosion test: Climate Tests. These tests consist of cycles of usually 24 hours (1 cycle) consisting of subjecting the samples to a sequence of climatic conditions of humidity, CNS and sudden temperature changes. The permanence of the samples in the climatic test chambers will depend on the applied coating, the specification of the end user and the type of test defined by each OEM, ranging from 1 to 30 cycles or more.

Covid-19 tests

The Inelca staff underwent tests last week, at its facilities in Sant Esteve de Sesrovires, to check if they are affected by Covid-19 and thus ensure the health of each of them. The results have been satisfactory, allowing the activity to continue safely.

In addition, the facilities have been adapted to the health protocols required by the authorities to minimize the risk of contagion and create a safe work space. These protocols require an effort by everyone, but the general attitude towards this new situation is collaborative and positive.

With all these actions carried out, the level and quality of the response is maintained to provide service to our customers who demand metal surface treatments.

ZnNi and Hydrogenation

One of the drawbacks of electrolytically deposited coatings is the possibility of hydrogenation.

In some of the phases of the coating application process, such as pickling or the deposition phase itself, hydrogen formation occurs on the metal surface to be coated as an auxiliary reaction.
This hydrogen, in monatomic form, can diffuse within the metal structure, producing fragility in it.

This monoatomic hydrogen diffused in the structure of the metal to be coated must be extracted, by means of thermal treatments, before it changes to diatomic hydrogen, at which time it is no longer possible to extract it by conventional dehydrogenation methods.

Zinc-nickel, due to the properties of the deposited layer and the deposition characteristics of that layer, has a much less tendency to hydrogenation than other Zn coatings and other alloys.

i) Properties of the deposited layer:
The deposited zinc layer is not very porous, preventing the hydrogen, which may have diffused in the metal structure to be coated, from being expelled if not by means of heat treatments. On the contrary, the zinc-nickel layer is much more porous and allows the possible diffused hydrogen to be evacuated before going to diatomic form.

ii) Deposition characteristics:
In the first moments of the deposition phase of the zinc-nickel coating, a small nickel layer is generated on the surface of the metal to be coated. This nickel acts as a catalyst in the reaction of the passage of monoatomic to diatomic hydrogen, so that, in this way, it does not diffuse within the base metal structure.

Advantages of ZnNi

Among all the surface coatings of zinc and its alloys, zinc-nickel has a number of advantages that makes it the leader:

i) Greater resistance to corrosion: The presence of 12 to 16% Ni in its structure, allows it to acquire the gamma phase, which gives it greater resistance to corrosion in salt spray and in climatic cycles compared to other applications from Zn.

ii) High resistance to wear: The hardness of the coatings prevents them from being damaged in the coating process itself, as well as in subsequent manipulations such as packaging, selections, transport, assembly, etc.

Layer hardness of various coatings:

Zn: 100 HV
ZnFe: 150-200 HV
ZnNi: 500-550 HV

iii) Reduced white corrosion formation: White corrosion in the ZnNi coating appears much less bulky than in other Zn coatings

Imagen corosión recubrimientos niquel

iv) Good stability at high temperatures: The ZnNi deposit is very stable at temperature, even keeping its properties at working temperature up to 200 ºC.

v) Low Hydrogen embrittlement: Due to the characteristics of the layer of the deposit formed, as well as those of the deposition process, ZnNi presents low Hydrogen embrittlement, as already indicated in standards with ISO 4042.

vi) Low corrosion by contact with Aluminum: Due to the difference in oxidation potentials of Zn and ZnNi, the latter has much less galvanic corrosion by contact with Al, which makes it a coating widely used in both the automotive and in other sectors.

Corrosion tests

A corrosion test involves the performance of laboratory experiments that simulate corrosive environments in order to determine the resistance of coated metals under controlled conditions.

The behaviour against corrosion of a metal is a joint property between its own characteristics and that of the environment that surrounds it, so since there is no valid test that covers all possible variables, it is necessary to define laboratory tests with established and controlled conditions , being the results that we will obtain both qualitative and quantitative.

Corrosion is defined as the attack of a metal by reaction with the environment gradually, this phenomenon implies a cost of between 1.5-3.5% of the gross national product. All metals with the exception of some metals such as Gold or Platinum are corroded to a greater extent in contact with atmospheric agents becoming Oxides.

The purpose of the corrosion tests is to be able to evaluate the long-term performance of various metals in an accelerated manner, which allows determining the behaviour of the various metals before the environmental exposure in a reduced time, although the purposes of the corrosion tests can be diverse (compare behaviour of metals and their alloys, selection of materials according to their use, study of materials….) the most important for anticorrosive coatings is to determine the anticorrosive effectiveness of metals deposited on the metal to be protected.

The results obtained in corrosion tests on coated steel parts allow us to compare results of various coatings under controlled conditions, being able to determine which coating behaves better when faced with external agents, but it should be taken into account that a corrosion test does not simulate the actual behaviour to which the conditions of the same are not 100% extrapolated to the actual exposure conditions, but must be used as a means of control according to standards and reproducibility check of the applied coatings.

INELCA opens a new production plant

As part of the company’s expansion and growth plan, INELCA will inaugurate this March a new plant next to the current one, in the same town of Sant Esteve de Sesrovires (Barcelona) where the main plant is located.

With a constructed area of ??2,200 m2, this plant will be a productive complement to the existing one that will help consolidate future projects and allow us to reach the technological challenges that lie ahead with industry 4.0.

INELCA imagen nueva planta producción INELCA imagen nueva planta producción INELCA imagen nueva planta producción

We are cardioprotected company

Imagen desfibrilador INELCA

Committed to the safety of people in the workplace, we have installed a defibrillator to protect the health of our employees currently working at our facilities in Sant Esteve de Sesrovires (Barcelona).

With the installation of the device, 6 people were trained in cardiopulmonary resuscitation (CPR) and defibrillator use.

The company is sensitized with the fact that in our country the risk of cardiovascular accident has a high prevalence. In this way we intend to preserve the well-being of the employees and of all the people who visit the facilities.

We believe that the current regulation on cardioprotection in work spaces should be modified and the installation of these devices in any work environment, regardless of the volume of employees, should be mandatory.

This action, clearly of improvement, can make the difference between saving or not saving a life because it allows a quick action in case of emergency.

Metal surface coating
Electrolytic coatings


Types of corrosion

Imagen trenes corrosión Inelca

Corrosion is defined as the deterioration of a material when interacting with its environment, the metal loses or decreases its physical and / or chemical properties. The corrosion process is accelerated by factors such as oxygen, humidity, temperature, chemicals and the change in the physical-chemical composition of the material.

Through the galvanizing process, a layer of zinc that acts as a sacrificial metal is deposited on the surface of the steel.

The different types of corrosion that occur in a steel treated with a coating of Zn and its alloys are presented below:

  • White corrosion or Zinc oxide: Zn + O2 à ZnO

Zinc is a very durable coating that acts as a sacrificial protection of steel, as it corrodes more slowly. White corrosion is a substance of that colour that can form on zinc when exposed to oxidizing environment. Optimum storage conditions are vital so that their properties are not affected.

  • Red corrosion or Iron corrosion: Fe + O2 à FeO

When the base metal is in contact with oxygen it oxidizes easily. This phenomenon causes iron to lose its properties and become fragile and brittle. That is why it is necessary to protect it by coatings.

Main objectives of the coatings

The benefits of metal surface coatings are so broad that they become indispensable for many areas.

There are coatings of different types which contribute some characteristics or others to the material on which they are deposited:

  • By means of electrochemical metal depositions, such as galvanized, Zinc alloys (Zinc Nickel, Zinc Iron, Zinc Cobalt, Zinc Cobalt Iron), tin plating, electrolytic nickel plating, decorative chrome plating, hard chrome.
  • Through chemical depositions, such as acid zinc and aluminum chromatizing.
  • Obtained by conversion, such as anodizing of aluminum and titanium, blued and phosphating.
  • Hot dip, such as galvanized, aluminized, tinned and leaded.
  • Metallization by projection or vacuum deposition.
  • Through plasma obtaining surface hard layers with PVD and CVD.
  • Paints, polyurethanes, electrophoresis, electrostatic powder, etc.
  • Coatings with PVC, rubber or Teflon plastics.

Depending on the type of coating used, the following improvements can be obtained:

  • Improvement of corrosion protection
  • Improvement of mechanical characteristics
    • Hardness
    • Wear resistance
    • Ductility


  • Improvement of specific properties
    • Weldability
    • Conformability
    • Electrical contact
    • A combination of several (color, abrasion resistance, friction coefficient, etc.)

Inelca expands its offer with a new installation of Zinc Flakes

Inelca Zinc Flakes

Inelca, as a company focused on customer service, is always in continuous evolution to offer excellence in service and an optimal response to customer needs. That is why in the last two years Inelca has been working with a new project in order to increase their production capacity and respond to these needs transmitted by their customers in the finishes of Zinc Flakes.

To this end, a new state-of-the-art Zinc Flakes line starts the activity at the end of July, provisioned by the Sidasa company, which has the latest technical improvements available in the market. It has a high productive capacity and is equipped with a robot that optimizes its performance greatly.

In the design of this line we have added our technical knowledge and our experience in lines of this type already in operation in Inelca, to those of our suppliers with the aim that the installation fulfilled all our specifications and requirements completely.

The improvements that this new facility brings us will be reflected in an increase in the Zinc Flakes capacity offer, both in the Zintek and Magni finishes, improvements in the quality of the final product and an improvement in the service rate offered to our customers. faster delivery times.

Beyond this new installation, Inelca continues working on new projects that will see the light in the near future that will involve new technical improvements and a further jump in the upward trajectory of the company.