Effect of Mn addition to core alloy on corrosion resistance of thin brazing sheet

Abstract

To investigate effect of additional Mn in thin brazing sheet core alloy on corrosion resistance, SWAAT and electrochemical measurements have been carried out with brazed Al-Mn-1.6 mass%Si alloys. Intergranular corrosion clearly occured in the alloys which Mn content is 1 mass% or less. In the case of these alloys precipitates of Si particle were observed at grain boundary, but they were not observed in grain after brazing. As a result, the potential difference between neighborhood of the grain boundaries and grain matrix became bigger. Therefore, selective dissolution occured at neighborhood of the grain boundaries which was lower solid solution of Si. On the other hand, intergranular corrosion were not observed in the alloys which Mn content is 1.6 mass% or more. In the case of these alloys fine precipitates of AlMnSi were observed in grain after brazing. As a result, the formation of Si-SDZ solute depleted zone by Si precipitation at grain boundary seen in the former alloys were inhibited. In conclusion, addition of Mn in thin brazing sheet had improving effect of corrosion resistance after brazing.

Influence of Silicon on Intergranular Corrosion for Aluminum Alloys

“…Al 合金の粒界腐食感受性に及ぼす Si の影響 Mg 系合金 6,10) は，粒界腐食感受性を有する．Al Si Mg 系 合金 6,7,9) および Al Si Mn 系合金 10,11) の粒界腐食感受性は， 373～873 K の熱処理によって増大する．これら粒界腐食の 原因は，Al Si Mg 系合金では，粒界上の Mg 2 Si 金属間化合 物の溶解 7,9) ，Al Si 系合金，Al Mn Si 系合金では，粒界に 沿った Si 欠乏層の溶解 6,8,10,11) Fig. 7 Optical micrographs of the cross section after anodic dissolution for Al 1.1Mn 0.4Si,  1.1Mn 0.8Si, and  1.1Mn 1.4Si at t HT ＝0, 8.64×10 4 , and 2.59×10 6 s. Fig.…”

Influence of Silicon on Intergranular Corrosion for Aluminum Alloys

“…11) Heat-treatment increases susceptibility to intergranular corrosion for AlSiMg 6,7,9) and AlSiMn. 10,11) This intergranular corrosion is caused by dissolution of either Mg 2 Si intermetallic compound at the grain boundaries in AlSiMg 7,9) or the Si-depleted layer along the grain boundaries in AlSi and AlMnSi alloys. 6,8,10,11) This means that the cause of the intergranular corrosion depends on the type of alloy.…”

“…10,11) This intergranular corrosion is caused by dissolution of either Mg 2 Si intermetallic compound at the grain boundaries in AlSiMg 7,9) or the Si-depleted layer along the grain boundaries in AlSi and AlMnSi alloys. 6,8,10,11) This means that the cause of the intergranular corrosion depends on the type of alloy. However, there are very few reports providing a systematic study of the influence of Si concentration in various alloys and the heat-treatment conditions on the susceptibility to intergranular corrosion.…”