Study On Fe-rich Phases Morphology And Alloy Properties Of Al-18Si% Alloy Containing Iron-rich

Hypereutectic Al-Si alloy has small density,good thermal conductivity,small coefficient of thermal expansion,good wear resistance,good corrosion resistance,good dimension stability characteristic,et al.Mechanical properties and machinability of this alloy can be improved by modification.This alloy is very suitable for making piston of engine.Therefore,hypereutectic A1-Si alloy is becoming ideality updated material of traditional eutectic Al-Si piston material.Fe was thought to be one of the most harmful impurities of Al-Si alloy.Cumulative increase of Fe in the repeated use of this alloy is a serious problem.At present,most research has focused on Fe as an impurity element in aluminum silicon alloy.It is rarely reported Fe as a specific alloy element added to hypereutectic aluminum silicon alloy to research microstructure and properties of high iron hypereutectic aluminum silicon alloy.In addition,the research of Fe-rich phase stable exit and have good morphology on engineering conditions is very important for hypereutectic aluminum silicon alloy's application.This paper takes Al-18Si-3Fe alloy as matrix and add different content of Mn,Cu,RE to research the influence of Fe-rich phase morphology and alloy properties by Olympus-tokyo metallographic microscope,DX-2500 X-ray diffractometer,S3400N scanning electron microscopy?with EDS?,Shenzhen new sans microcomputer control electronic universal testing machine,HVS-1000 automatic microhardness tester and other modern testing technology.The experimental results indicate that:?1?Adding 3%Fe in Al-18Si alloy will form a large number of double strips shape Fe-rich phase Al₃FeSi₂.Average tensile strength of Al-18Si alloy dropped from 150 MPa to113.3 MPa.?2?Adding Mn in Al-18Si-3Fe can perfect the morphology of Fe-rich phase.Otherwise the size of primary silicon and eutectic silicon and Fe-rich phase decreased.The tensile strength of alloy reached a maximum of 135.2 MPa when Mn content reaches 3%.The size of primary silicon and iron-rich phase increased and the tensile strength of alloy began to fall when Mn content more than 3%.The increase of Mn cannot fully inhibit strips Fe-rich phase appear under high cooling rate.?3?Adding 5%Cu to Al-18Si-3Fe-3Mn alloy can increased alloy strength from 135.2MPa to 168.8 MPa.Fe-rich phase morphology mainly as fishbone was uniform and its size reduced.?4?The morphology of primary silicon and eutectic silicon has been improved after adding RE in Al-18Si-3Fe-3Mn-5Cu alloy.Even if 0.2%RE also promote the emergence of needle Fe-rich phase,and there are acicular structure Al₂?SiCu?₂RE appear,the tensile strength of alloy decreased to about 137 MPa.The size of Fe-rich phase and primary silicon began to increase when adding more than 0.35%RE.?5?T6 heat treatment can turn the needle eutectic silicon into globular form,also round the edges and corners of primary silicon,Al₃FeSi₂ has dissolved phenomenon.Cu element has been uniform distribution.The edges and corners of Fe-rich phase became obtuse weakly.But the needle structure Al₂?SiCu?₂Re almost has no change.The tensile strength of Al-18Si-3Fe-3Mn-5Cu alloy increased to 193.1MPa and Al-18Si-3Fe-3Mn-5Cu-xRE alloy increase to 181 MPa.?6?Whether adding RE elements had significant effects on the tensile strength of Al-18Si-3Fe-3Mn-5Cu alloy.The content of RE elements has no obviously effect on tensile strength of this alloy.RE elements does more harm than good in this alloy.