Corrosion Behavior of Al Alloys By Additive Manufacturing
Authors: Estupiñan-Lopez Francisco , Gaona-Tiburcio Citlalli , Cabral-Miramontes Jose A. , Treviño-Morales Raul , Almeraya-Calderón Facundo 
Published: February 2020

INTRODUCTION

The alloys of (Mg-Si) are not among the most resistant aluminum alloys, but these represent a large part of the aluminum products in the world (approximately 20%), however, they are prone to failure by corrosion. Aluminum tends to be attacked locally in particular by crevice (crevice corrosion) and in areas of stagnation, in which passivity disappears.
In recent years, 3D manufacturing technology has become relevant in the manufacturing processes and the printing of alloys has not been the exception. Among the benefits that can be obtained is an improvement in the union between different materials, the concentrations of mechanical stress can be reduced, increasing the life component, among others. The alloys of Al-Si10-Mg are the preferred choice of material for die-casting applications, this is due to the properties with which silicon (Si) contributes, among them, the increase of the fluidity, decrease of the shrinkage of In addition, solidification increases the corrosion resistance as the Si content increases. The role of magnesium (Mg) in Al-Si alloys provides the property of making them bondable and achieving considerably higher strength and hardness values, in addition to improving machinability.
The manufacture of Al-Si10-Mg alloys by additive manufacturing is a powder bed process, where a laser or electron beam traces the pattern of the part in a layer of fine powder and a new layer of powder is deposited on the previous. The beam traces the pattern of the second layer, and joins the melted zones of the two layers. The process continues until the part is finished.

EXPERIMENTAL METHODOLOGY

In this work AlSi10Mg aluminum alloys were manufactured by additive manufacturing in the form of 1*1*2 cm cubes with a "SLM 280 HL solutions GmbH" equipment and evaluated by electrochemical tests. The samples were placed with copper wire to make the electrical connection, roughed with # 600 silicon carbide sandpaper and dried with ethanol before the electrochemical tests. The electrochemical techniques used were Electrochemical Noise (RE) and Linear Polarization Resistance (RPL) in electrolytes of distilled water (H2O) and sodium chloride (NaCl) at 3.5% by weight.

RESULTS

The time series in potential and current in H2O showed an unstable corrosion potential during the 120 hrs of exposure and the transients decrease their amplitude as the exposure increases. In the current time series, the transients moved away from the average at the beginning of the exposure and subsequently decrease.
The time series in potential and current in the NaCl solution, it was observed that transients in potential tend to decrease in their amplitude by increasing the exposure time. The corrosion current density tended to increase when the exposure in the electrolyte increased and the transients did not move away from the mean.
The RPL results in distilled water presented similar corrosion velocity values in the different immersion times, without showing a linear increase in their values; while for the NaCl solution average values of approx. 0.04 mm / year.

CONCLUSIONS

In the graphs of electrochemical noise and polarization curve, a pitting corrosion mechanism is identified in the distilled H2O solution, while in the NaCl solution pitting at a greater depth is observed.
The alloy AlSi10Mg in NaCl tends to present corrosion in the thermally affected area by the fusion laser.