Local Corrosion Behavior of Additive Manufactured AlSiMg Alloy Assessed by SEM and SKPFM

Abstract

The local corrosion behavior of additive manufactured AlSiMg specimens was studied using the SEM and SKPFM techniques. A morphological characterization of corroded areas revealed that crystallographic pitting developed in the aluminium grains inside the melt pool borders, from where corrosion spread to adjacent zones. The local Volta potential analysis showed that there is a close relation between the cellular grain size and the potential difference between the silicon and the aluminium phase. SKPFM measurements explained why the melt pool borders were more severely attacked by corrosion than other regions in the surface of the AM specimens. In regions with larger and coarser microstructures, greater potential difference between the phases was found, which represents a higher driving force for galvanic corrosion.

Corrosion of Additively Manufactured Alloys: A Review

“…The SLM AlSi10Mg specimens presented an apparently better corrosion resistance than their cast counterparts (albeit only through evaluation by corrosion potential values, which are not a measure of corrosion rate). If the results are to be considered reliable, then they may be in agreement with Leon, et al, 89 though they contradict the results obtained by Revilla, et al 88 In contrast, Fathi, et al, 91 suggested that grinding the SLM AlSi10Mg specimens was detrimental to the continuous oxide layer formed on the AP specimen surface, inconsistent with the findings of Leon, et al 90 Therefore, the role of surface finish (i.e., roughness) on the corrosion of SLM AlSi10Mg remains unclear. This lack of clarity is exacerbated by a lack of standardized testing by many authors, and also by the use of an arguably aggressive electrolyte for such an alloy, which might obscure surface finish effects.…”

“…The effect of the use of recycled powder, laser scan passes, and layer thickness on the corrosion of the AlSi10Mg produced by SLM was studied by Revilla, et al 88 In the study, the corrosion potential (E corr ) values derived from potentiodynamic polarization of the cast and SLM AlSi10Mg specimens were similar, with values ranging between −0.7 V Ag/AgCl and −0.6 V Ag/AgCl (Figure 4). The corrosion characteristics observed for SLM and cast AlSi10Mg were correlated by Revilla, et al, who observed similar microstructure and composition.…”

“…The findings of such studies are summarized in Table 3. 79,[88][89][90][91][92][93][94] Some of the pertinent results summarized in Table 3 are discussed in more detail below, allowing for mechanistic aspects to be examined, but also illuminating that in many cases there are contradictory results from different studies. In cases where only a very small number of studies exist, contradictory conclusions between studies are the present hallmark of the status in the understanding of corrosion for many AM-prepared alloys.…”

“…The OCP and potentiodynamic polarization response of SLM (S1 to S5) and cast (CA) AlSi10Mg specimens in a 0.1 M NaCl: (a) open-circuit potential and (b) potentiodynamic polarization. Adapted from Revilla, et al,88 with permission from The Electrochemical Society, Copyright 2017.…”

Corrosion resistance in chloride solution of the AlSi10Mg alloy obtained by means of LPBF

“…In addition, the presence of silicon inside the oversaturated α‐Al phase increases its electrochemical potential. Revilla et al measured the Volta potential differences between Al and Si inside and outside the melt pool borders of specimen without heat treatment. The authors concluded that such difference is much higher inside the melt pool border than outside.…”