# Comparison of Two Intergranular Corrosion Tests on EN AW-6016 Sheet Material
## 5 Conclusions  
Two different IGC tests were carried out on EN AW-6016 car-body sheet material. Both tests varied in sample preparation, duration, testing solution composition, and solution amount while the determination of the IGC depth via OM was the same. Following a proposal by the GDA, the ISO 11846:1995's testing parameters were modified. The solution amount and acid concentration were varied. It was seen that a variation of these parameters resulted in deviations in the IGC depth results up to 25%. It is therefore recommended to adhere to defined values for these parameters for a reliable comparison of test results, e.g., from different materials or different thermal treatments. It was further seen that PV1113 tests resulted in a corrosion speed up to 11 times higher than the ISO 11846:1995-based tests. These IGC speed differences were related to the HCl/NaCl ratio of the respective test solutions. The proportionalities of the IGC speeds between the analyzed samples were almost identical to the HCl/NaCl ratio proportionalities of the respective test solutions. Differences resulted from an additional pitting-corrosion-like attack in PV1113-tested samples. PV1113 has a time tolerance of 0.5 h for the duration of the test which is twice as high as for ISO 11846:1995, even though the testing time of the latter test method is 12 times longer. Considering the much higher corrosion speed of the PV1113, a difference of \(\sim\)40 \(\upmu\)m (or \(\sim\)20%) for an EN AW-6016 could appear when applying the maximum temporal tolerance. Together with a determined deviation of 9% in the corrosion depth between both tested PV1113 samples, a sum-up could result in a possible deviation of 29% in other experiments. Such a high systematical deviation makes the comparison of different tested materials difficult if not impossible. The longer duration of ISO 11846:1995 is therefore preferred to minimize the error of eventual testing time differences. The much lower corrosion speed of ISO 11846:1995 is further helpful in this regard. It is therefore concluded that ISO 11846:1995 tests should be preferred if enough time is given to carry out such prolonged testing. This would then lead to IGC results that are better comparable with each other and further allow the determination of proper IGC depth thresholds an Al alloy must withstand during testing. It is seen that IGC susceptibility is less a material constant but is dramatically influenced by the testing conditions. This makes the comparability of different testing methods difficult. It is therefore emphasized that careful experimental planning is necessary to allow for reproducible results. Furthermore, it needs to be considered how IGC suscep \begin{table}
\begin{tabular}{c c c} \hline \hline
**Compared Parameters** & **Max. Deviation (\%)** & **Max. Deviation (\(\upmu\)m)** \\ \hline
**Solution amount variation (x.1/x.2/x.3)** & 1.29/7.61/26.74 & 2.95/19.13/72.85 \\
**Acid concentration variation (1.x/2.3)** & 20.07/16.44 & 50.13/42.99 \\
**Max. observed standard deviation (1.1)** & 5.9 & 13.06 \\
**PV1113 variation (3.1 and 3.2)** & 9.02 & 17.24 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Calculated deviations of the average corrosion depths. The numbers in brackets relate to the compared samples. tibility can be evaluated when other corrosion mechanisms (as the formation of cavities in the PV1113 test) are initiated. In the given case of PV1113, it is assumed that other corrosion mechanisms occurred due to the much more potent testing solution compared to ISO 11846:1995. This work aims to highlight concerns regarding IGC test setups and the evaluation of test results. It aims to initiate more careful thinking and planning of IGC experiments. The overall aim should be to achieve higher comparability of IGC results, which would allow for a better evaluation of a possible material's lifetime with regard to this special type of corrosion. Conceptualization, L.M. and P.D. ; validation, L.M. and P.D. ; investigation, I.Z. ; writing--original draft preparation, P.D.