Modulation Of Iron Phase Morphology Of ADC12 Secondary Aluminium Alloy

ADC12 aluminium alloy as a kind of recycled aluminium alloy is widely used in the production of automotive parts,its application prospect cannot be ignored,however,the existence of impurities in the alloy has become the biggest obstacle to limit its use,among which Fe element is one of the main impurities,its in the alloy solidification process is easy to form iron-rich phase.Therefore,how to remove or transform the harmful iron-rich phase is the key to solve the problems of poor quality and low added value of recycled aluminium.In this paper,the effect of Fe content on alloy properties was firstly investigated by using metallographic microscopy,quantitative metallographic statistical analysis,scanning electron microscopy(SEM/EDS),XRD and other analytical means,combined with mechanical tensile tests,and then adding Mo,Mn,Sr and La elements to the iron-rich phase without changing the Fe content.The effect of the addition of single and composite elements on the Fe-rich phases and properties of the alloy was investigated.The specific findings of the study are as follows:(1)In ADC12 aluminium alloy,with the increase of Fe content from 0.8% to 1.3%,the evolution of the morphology of the Fe-rich phase is as follows: compact Chinese script,Chinese script & dendritic,Chinese script & dendritic & needle-like,needlelike & Chinese script,needle-like,the area fraction of Fe-rich phase gradually increases and the length keeps growing;with the rise of Fe content,the tensile strength and elongation of the alloy start to change,where α-Fe generation and growth have little effect on the mechanical properties of the alloy,while the appearance of β-Fe leads to a significant decrease in the mechanical properties of the alloy.(2)The addition of Mo to the alloy can generate Al-(Fe,Mo)-Si intermetallic compounds,which achieve the purpose of promoting the generation of α-Fe phase and inhibiting the growth of β-Fe phase.The α-Fe phase generated includes multilaterally shaped primary α-Fe and eutectic α-Fe in the shape of a Chinese character(dendrite),but the addition of Mo alone does not completely transform the β-Fe phase into the α-Fe phase;the morphological evolution of the Fe-rich phase during the rise in Mo content from 0% to 0.4% is as follows: needle-like,needle-like & polygonal,polygonal& needle-like & Chinese script,polygonal & needle-like & dendritic & Chinese script,polygonal & needle-like & dendritic;the addition of Mo content improves the mechanical properties of the alloy,and when the Mo content reaches 0.3%,the tensile strength and elongation increase by 19.14% and 61.2% respectively compared to the original alloy.(3)The addition of Mo and Mn can inhibit the generation of β-Fe phase and promote the growth of α-Al(Fe,Mo,Mn)Si phase;The results of the analysis of extreme variance and analysis of variance showed that the addition of Mo can strongly promote the generation of α-Fe phase,which can play a more significant role compared with Mn.The compound addition of Mo(0.3%)and Mn(0.2%)basically transformed the needlelike β-Fe phase in the tissue into α-Fe phase,and the tensile strength and elongation of the alloy increased by 37.86% and 100.45% respectively compared to the original alloy,but the excessive addition would increase the area of α-Fe phase,thus adversely affecting the mechanical properties.(4)The simultaneous addition of Sr and La can refine the α-Al grain,and the compound addition of Mo,Sr and La can promote the generation of α-Fe phase and inhibit the growth of β-Fe phase,where the addition of Sr and La can shorten the length of β-Fe phase and significantly improve the mechanical properties of the alloy;the results of the polar difference analysis show that the significance of the effect of the three elements on the properties of the alloy is: Mo> Sr> La.The optimum element additions are Mo%=0.2wt.%,Sr%=0.2wt.% and La%=0.2wt.%.