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

Florentino Alvarez-Antolin,Juan Asensio-Lozano,Alejandro Gonzalez-Pociño,Alberto Cofiño-Villar

doi:10.3390/met10050620

Abstract

In the as-cast state, Al–Mg–Si alloys are not suitable for hot forming. They present low ductility due to the presence of intermetallic β-AlFeSi particles that form in the interdendritic regions during the solidification process. Homogenization treatments promote the transformation of these particles into α-(FeMn)Si particles, which are smaller in size and more rounded in shape, thus improving the ductility of the material. This paper analyses the influence of various solution treatments on the transformation of β-AlFeSi particles into α-(FeMn)Si particles in an Al 6063 alloy. Their effect on different ageing treatments in the 150–180 °C temperature range is also studied. An increase in the solution temperature favours greater transformation of the β-AlFeSi particles into α-(FeMn)Si, dissolving a greater amount of Si, thereby having a significant effect on subsequent ageing. We found that as the dwell time at a temperature of 600 °C increases, the rate of dissolution of the Fe atoms from α-(FeMn)Si particles exceeds the rate of incorporation of Mn atoms into said particles. This seems to produce a delay in reaching the peak hardness values in ageing treatments, which warrants further research to model this behaviour. The optimal solution treatment takes place at around 600 °C and the highest obtained peak hardness value is 104 HV after a 2 h solution treatment at said temperature and ageing at 160 °C for 12 h.

Highlights

Aluminium alloys usually have iron as a common impurity
This paper thethe influence of solution treatments on theon transformation of β-AlFeSi particles paperanalyses analyses influence of solution treatments the transformation of β-AlFeSi into α-(FeMn)Si particles and their possible influence on different ageing treatments carried out in the particles into α-(FeMn)Si particles and their possible influence on different ageing treatments carried
The main conclusions are: (1) The Fe/Si atomic ratio increased with increasing solution treatment temperature from 550 to

Summary

Introduction

Aluminium alloys usually have iron as a common impurity. The maximum equilibrium solubility of Fe in solid aluminium is very low. The particles present in Al–Mg–Si alloys during solidification are mostly β-AlFeSi (generally the β-Al5 FeSi phase), α-AlFeSi (generally the α-Al8 Fe2 Si phase) and Mg2 Si [1,2,3] These alloys are not suitable for hot forming processes in the as-cast state or in processes of intensive deformation, as occurs in extrusion. Their ductility is too low, mainly due to the presence of intermetallic β-AlFeSi particles that locate at interdendritic regions, giving rise to the occurrence both inside the α-Al grains and at their grain boundaries after solidification is completed [4].

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