Effect of the chemical composition and high-temperature heating simulating a brazing operation on the structure and mechanical properties of Al – Mn (–Mg) Alloy Sheets. Part I

Abstract

Development of a novel AMts-type alloy with high corrosion resistance and good strength is an actual task for application in heat-exchangers which are used in new aircraft products. A thermodynamic simulation of phase composition in Thermo-Calc software was used to choose experimental alloys of Al – Mn system taking into account required solidus temperature for brazing. It is shown that the main influence in reducing of solidus temperature for investigated alloys is caused by magnesium and copper, and the less influence is caused by iron. Evaluation of strength degradation of cold-rolled sheets from experimental Al – Mn alloys after high-temperature heating simulating brazing operation showed that the lest reduction of strength is observed for alloys, which contain Fe and Si. A dependence of residual strength of sheets from (Fe + Si) content and amount of α-phase (Al15(Mn, Fe)3Si2) is determined. The peculiarities of the microstructure and mechanical properties of commercial clad sheets from a new Al – Mn – Mg alloy for application in aircraft heat-exchangers are investigated. By means of transmission electron microscopy and EDX-analysis it was concluded that the alloy in H24 temper has subgrain structure, which includes precipitations of dispersoids with spherical form, which are associated to α-phase (Al15(Mn,Cr, Fe)3Si2). Magnesium, which is used as main alloying element in the alloy, is almost completely dissolved in aluminum matrix, providing solid solution strengthening effect. Clad sheets from the alloy provide a high corrosion resistance (IGC < 0,08 mm) and good level of mechanical properties in H24 temper (UTS ≥ 180 MPa, YS ≥ 170 MPa, El. ≥ 10 %) and also good residual strength after brazing (UTS ≥ 150 MPa).This research was carried out as part of the following comprehensive research project: Light High-Strength Corrosion-Resistant Weldable Alloys and Steels, Including Alloys and Steels with High Fracture Toughness (Strategic Development of Materials and Processing Techniques in the Period till 2030).The authors would like to thank S. V. Samokhvalov and S. V. Shurtakov from Core facility “Climatic tests” — VIAM for research and advisory support and for their great contribution to the experiments apnd analysis of the obtained results.