Study On Preparation And Properties Of Magnesium-based Ceramic Core

With the continuous development of manufacturing industry,the demand for the properties of castings is increasing.Alloy steel castings are widely used and some of them have complex inner cavity structure,which brings difficulties to casting process design and production.However,there are few studies on ceramic cores for alloy steel.According to the analysis of material characteristics,it has obvious advantages to make alloy steel ceramic cores with magnesium oxide.In this paper,magnesium oxide was used as matrix material,Al₂O₃,TiO₂ and their combination were used as mineralizer,green samples were prepared by pressing molding and hot injection moulding,and then magnesium oxide-based ceramic cores were prepared by sintering according to defined sintering process.The effects of mineralizer,sintering process and forming method on the structure and mechanical properties of the cores were studied,and the solubility of sintered core in acetic acid solution was tested.Pressing molding was used to prepare the green samples.Magnesium oxide was used as matrix material,and Al₂O₃ was used as mineralizer to promote the sintering of magnesium oxide ceramic cores.The Al₂O₃ mineralizer promotes the sintering of the cores effectively.When the content of Al₂O₃ is 1%,the sintering temperature is1340°C and the holding time is 0.5 h,the core's comprehensive properties is the best.The flexural strength at room temperature is 24.95 MPa.At this time,the porosity is27.04%,the sintering shrinkage is 0.88%,and the solubility value is 0.084 mm/h.With TiO₂ as mineralizer of ceramic cores can also promote the sintering of the cores.The strengths of magnesium-based ceramic cores with TiO₂ mineralizer are obviously higher than that of magnesium-based ceramic cores with Al₂O₃ mineralizer at the same sintering temperature,but the solubility value is lower.When the content of TiO₂ is 2%,the sintering temperature is 1320°C and the holding time is 0.5 h,the core has the best comprehensive properties.The flexural strength at room temperature is 29.24 MPa.At this time,the porosity is 25.75%,the sintering shrinkage is 1.12%,and the solubility value is 0.125 mm/h.With Al₂O₃ and TiO₂ as mineralizer of cores,when the content of Al₂O₃ is 2%,the content of TiO₂ is 2%,the sintering temperature is 1300°C and the holding time is0.5 h,the core has the best comprehensive properties.The flexural strength at room temperature is 22.07 MPa,the porosity is 26.62%,the sintering shrinkage is 0.96%,and the solubility value is 0.088 mm/h.When Al₂O₃ and TiO₂ are used as mineralizers,the comprehensive properties of ceramic cores are similar to those of Al₂O₃ alone,but lower than that of TiO₂ alone.The effects of mineralizers and their additions on the properties of ceramic cores were studied by hot injection moulding.When the content of TiO₂ is 2%,the sintering temperature is 1320°C and the holding time is 0.5 h,the core has the best comprehensive properties.The flexural strength at room temperature is 20.95 MPa.At this time,the porosity is 31.38%,the sintering shrinkage is 1.08%,and the solubility value is 0.126 mm/h.Comparing with the pressed samples with the same composition,the flexural strength decreases by 28%,the porosity increases by 21%,the sintering shrinkage decreases by 3%,and the change of solubility is not obvious.