Influence Of Microalloy And Modification On Microstructure And Mechanical Property Of ZL114A Alloy

Cast aluminum alloys are widely used in automotive parts,and comparing with traditional ferrous metal aluminum alloy can decrease 30%⁴0%of the weight.This can save oil resources and protect environmental.However,the poor mechanical properties of ZL114A alloy can not content the demand for material properties of automotive parts.In order apply to the automotive parts.Therefore,improving the mechanical properties of the alloy,so that it can be applied to automotive parts preferably to satisfy the needs of modern lightweight.Today,changing the alloy composition content and adding the refining modifier is the main means to improve the properties of the alloy.Fistly,in order to achieve the optimal Mg content,different Mg content had been added to ZL114A and revealed the effect of Mg on the microstructure and properties of them.Then,changing the addition amount of Al-5Ti-B and Al-10Sr modifier and studying the effect of microstructure and properties of refiners to achieve optimal contentIn this paper,ZL114A alloy is used as the research object.And the optical microscope,scanning electron microscope and electronic universal testing machine have been used to studied.The results show that when the content of Sr is 0.04 wt.%,with the increase of Mg content,the Mg element is distributed at the front edge of the solid-liquid interface of eutectic silicon during solidification,which hinders the growth of eutectic silicon and drives them into particles.The morphology of them gradually changes from long strips and lumps to fibrous ones,and the spacing of secondary dendrite arms first decreases and then increases.When the amount of Mg is0.8%,the secondary dendrite arm spacing of the alloy reached a minimum value of 5.179?m.When the Mg content is 1.2%,the tensile strength and the elongation of the alloy inthe as-cast state is 198.8 MPa and 4.575%respectively.After heat treatment,the tensile strength and the elongation reach to 342.3 MPa and 4.657%.Besides,the Mg₂Si strengthening phase increasing with the adding of Mg.As a result of them the pinning dislocation effect is enhanced,the tensile strength of the alloy is increasedand the elongation is lowered eventually.When the amount of Mg and Sr was kept at 1.2 wt.%and 0.04 wt.%,respectively.As a result the interaction between B and Sr element,with increasing of the of Al-5Ti-B refiner,eutectic silicon size gradually increases.Small amount of long and strip-shaped eutectic silicon began to appear in the alloy when Al-5Ti-B refiner reach 1%,meanwhile the secondary dendrite arm spacing first decreased and then increased.The tensile strength of the alloy first increase and then decrease,the elongation has no obvious law.When the addition amount of Al-5Ti-B refiner is 0.5%,the refining effect of the alloy is the best.At this condition,the heterogeneous nucleation TiAl₃ phase is formed reachs the maximum,and the secondary dendrite arm spacing of the alloy is 5.265?m.The tensile strength and elongation of as-cast condition is 204.7 MPa and 4.710%,after heat treatment they achieve 349.2 MPa and 4.731%respectively.Keeping the addition amount of Mg and Al-5Ti-B refiner at 1.2 wt.%and0.5 wt.%.In this condition,eutectic silicon refined due to the low content of Sr can change the growth mechanism of them.However,when the content is high,poisoning phenomenon will occur.As a result of them,the eutectic silicon first decreases and then increases.SrB₆ is formed through the reaction of Sr and B when the addition of the Sr element,so the refinement effect of B on?-Al is weakened,and the spacing of the secondary dendrite arms increase gradually.The tensile strength and elongation of the alloy increases first and then decreases.When the amount of Sr element is 0.02%,the alloy achieves the best metamorphism effect.The tensile strength of the alloy is 213.3 MPa and the elongation is 5.025%at as-cast condition,after heat treatment they reach 357.1MPa and 5.423%respectively.