<i>In Situ</i> Isothermal Calorimetric Measurement of Precipitation Behaviour in Al-Mg-Si Alloys

Abstract

Isothermal time-temperature-precipitation (TTP) diagrams deliver important material data like temperature and time ranges critical for precipitation. During the last years an in-situ calorimetric method to record continuous cooling precipitation diagrams has been developed to application level by our group. However, isothermal TTP-diagrams were still determined by ex-situ analyses only. In this work in-situ measurements of precipitation reactions were carried out during isothermal soaking. Therefore the whole heat treatment cycle was performed in a differential scanning calorimeter (DSC). Al-Mg-Si-alloys 6063 and 6005A were analysed. Solution annealing and overcritical quenching to several temperatures between 450 °C and 250 °C was followed by isothermal soaking. Based on the heat flow curves during isothermal soaking TTP-diagrams were determined. Further microstructure investigations by scanning electron microscopy and hardness tests after artificial ageing were performed. Both alloys show similar results. In the TTP-diagramms three so-called ”C-curves” could be observed. Every C-curve is expected to represent precipitation of a different phase. Hardness and microstructure investigations correspond with the data of the TTP-diagramms.

Precipitation Stages and Reaction Kinetics of AlMgSi Alloys during the Artificial Aging Process Monitored by In-Situ Electrical Resistivity Measurement Method

“…For example, the relative volume fraction of the precipitates can be simply calculated by its initial, real-time, and final resistivity values (ρ 0 , ρ t , ρ f ) through the expression: f r = (ρ 0 − ρ t )/(ρ 0 − ρ f ) [29,31]. It is similar to those using the data obtained by DSC and isothermal calorimetry experiments [19,20]. Moreover, it is suggested that this method would be also useful for analysis of the cluster and GP zones evolution, since the variation of resistivity is highly related to them [24].…”

“…Significant achievements in the characterization of the precipitation behavior of AlMgSi alloys have been reached since the end of last centenary, with the assistance of advancing technologies, like High Resolution Transmission Electron Microscopy (HRTEM) [5][6][7][10][11][12][13], Atom Probe Tomography (APT) [1,[13][14][15][16][17], Differential Scanning Calorimetry (DSC) [18][19][20], electrical resistivity measurements [21][22][23][24][25][26], Phase Field Crystal (PFC) modeling [4,24], etc. The precipitation sequence has been established and gradually accepted as: supersaturated solid solution (SSSS)→clusters/GP…”

Analysis of Different Solution Treatments in the Transformation of β-AlFeSi Particles into α-(FeMn)Si and Their Influence on Different Ageing Treatments in Al–Mg–Si Alloys

“…This cooling rate should be as high as possible in order to achieve the maximum supersaturation of Si and Mg in solid solution [24,[30][31][32]. The most sensitive temperature range at industrial cooling rates seems to be between 450 and 250 • C [24,31,33]. Prolonged solubilization treatments are necessary in order to ensure the total dissolution of the Mg 2 Si formed in the cooling after chemical homogenization.…”