Effect Of CaO Addition On Microstructure And Properties Of AZ91 Alloy For Automotive Structural Parts

In this paper,AZ91,which is commonly used in industrial production,is used as a raw material,and CaO powder is added in a molten state.The effect of CaO content on the microstructure and properties of the alloy was investigated.Determine the optimal composition and explore the stirring process of alloy melting.Provide research data and ideas for CaO refinement of magnesium-aluminum alloys.Firstly,the effects of different contents of CaO on the microstructure,mechanical properties and corrosion properties of AZ91 alloy were investigated.By comparing the experimental results,it is concluded that when the CaO addition amount is0.7wt.%,the microstructure and properties of the AZ91 alloy are ideal.Then,the effects of CaO on the microstructure and properties of AZ91 alloy under normal mechanical agitation and under high shear plus ultrasonic agitation were studied.It is concluded that the average grain size of AZ91-0.7wt.%CaO alloy is reduced by86.8%compared with AZ91 alloy after adding 0.7wt.%CaO modifier under high shear and ultrasonic stirring,maximum compressive strength and compressive yield strength increased by 82.1%and 67.3%respectively compared to AZ91 alloy.Finally,the properties of AZ91-0.7wt.%CaO alloy and AZ91-1.0wt.%RE alloy were prepared by comparing CaO and Ce-La Misch Meral as refiner.Compared with the AZ91 alloy,the addition of CaO and rare earth reduced the grain size from 237.290μm to 31.390μm and 27.49μm,respectively.The second phase ratio decreased from 19.029%to11.414%and 8.644%,respectively,and the effect of CaO was only 0.6%and 2.77%lower than that of rare earth,respectively.The maximum compressive strength and yield strength of AZ91-CaO alloy and AZ91-RE alloy are 82%and 67%,90%and112%higher than those of AZ91 alloy,respectively,due to grain refinement.At the same time,the compression ratio is also improved.Electrochemical experiments and salt spray corrosion experiments also confirmed that the two alloys have similar properties.Although the mechanical properties of AZ91-CaO alloy are slightly lower than that of AZ91-RE alloy,CaO is more suitable as a candidate fine material for rare earth elements for mass production in the 21^stcentury from the perspective of cost-saving and energy-saving vehicle energy saving.