Effect Of Mn Content On The Microstructure And Property Of A356Alloy

Aluminum-silicon alloys are now being employed with growing frequency in theautomotive industry. The extended application of these alloys for automotive componentsforces us to understand the effects of Mn content on the microstructures and properties ofthese cast alloys more deeply. However, the present research on the iron-rich phase ofA356alloy is only limited to some specific conditions. And the required Fe/Mn ofchanging the iron-rich phase morphology is not clear by far. Moreover, the relationshipbetween the morphology of the iron-rich phase and Mn content has not been reported.In this paper, the A356alloy containing0.13wt%Fe was used as raw adding Al-10Srand Al-5Ti-B for modification and refinement. In addition, different amounts of Al-10Mnwere added to change the iron-rich phase morphology. Then prepare the A356alloy ingots.The morphology was investigated. Moreover, the effects of remelting and heat treatmenton the iron-rich phase morphology of the A356alloy were studied. The phase compositionof the A356alloy with different Mn content was researched by X-ray diffraction. And theiron-rich phase morphology of the A356alloy with different Mn content was studied byoptical microscopy and scanning electron microscopy (SEM). Additionally, therelationship between the Mn content and the mechanical properties of the A356alloy wasinvestigated through tensile tests method.The results indicated that when0.5wt%Al-5Ti-B,0.5wt%Al-10Sr and differentamounts of Al-10Mn alloy were added into the A356alloy during melting at740°C for10minutes, most of the coarse acicular β-Fe phase has transformed into Chinese script(orFishbone-like) α-Fe phase, and the quantity of α-Fe phase grows up with the increase ofthe Mn content. The length and width of the acicular β-Fe phase decreased44.13%and43.89%respectively when the Mn content was0.08wt%compared with the alloy withoutMn. The transformation rate of β-Fe phase was up to95.17wt%when the Mn content was0.16wt%. After a kind of special heat treatment process, the iron-rich phase of the A356alloy disappeared. The tensile test results indicated that, the ductility and the tensilestrength reaches the peak value when the Mn content was up to0.08wt%. And the furtheraddition of Mn content did not affect the mechanical properties obviously. The ductility and tensile strength of the alloy were improved after the heat treatment.