Enhancing mechanical properties of twin-roll cast Al–Mg–Si–Fe alloys by regulating Fe-bearing phases and macro-segregation

Abstract The existence of coarse Fe-bearing phases and macro-segregation under the twin-roll casting (TRC) condition has always been a restrictive factor for the preparation of high-performance Al alloys. In this work, the effect of Mn contents on the formation of Fe-bearing phases, macro-segregation behavior and mechanical properties of TRC Al-0.5Mg-0.7Si-0.1Fe-xMn (x = 0, 0.1, 0.3 and 0.5 wt.%) alloys have been investigated. The macro-segregation region in the as-cast 0Mn alloy is found to contain coarse secondary phases consisting of Al, Fe, Mg and Si. In as-cast 0.1Mn and 0.3Mn alloys, macro-segregation has been alleviated due to the transformation of π-AlFeMgSi phase to α-Al(FeMn)Si phase, as a result of the inhibited peritectic reaction to form the π-AlFeMgSi phase by the addition of Mn. However, with further increasing the amount of Mn, coarse intermetallic compounds at the center region tend to form in the 0.5Mn alloy, which aggravates macro-segregation again. The 0.1Mn alloy exhibits a better combination of yield strength (287 MPa) and elongation (18.9%) than that of the 0Mn alloy (274 MPa, 15.9%) under the artificial aging condition. The higher yield strength of the 0.1Mn alloy is mainly due to the formation of fine α-Al(FeMn)Si particles that make a strong contribution to dispersion strengthening. This work provides a reference for weakening macro-segregation via regulating Fe-bearing phases, which is of great importance in developing AA6xxx series TRC alloys with high performance.