Al-3B变质对铸造Al-10Si合金显微组织与力学性能的影响

采用Al-3B对铸造Al-10Si合金进行了变质处理,运用非平衡相图和杠杆定律分析了变质处理Al-10Si合金显微组织变化规律,研究了变质处理对合金力学性能的影响。研究表明,Al-3B变质处理使铸造Al-10Si合金的凝固过冷度减小;当变质温度一定时,随着Al-3B加入量增加,铸造Al-10Si合金组织中初生α-Al相体积分数呈现先增加后减少的变化趋势,当加入0.25%Al-3B时,初生α-Al相的体积分数达到最大值42.8%,且合金中的Si相呈细小短片状或短棒状;当变质剂加入量一定时,随着变质温度的增加,初生α-Al相的体积分数逐渐增加。Al-3B变质剂加入量对Al-10Si合金抗拉强度和延伸率影响的规律与其对合金组织中初生α-Al相体积分数影响的规律完全一致,初生α-Al相体积分数和共晶Si尺寸和形态对合金综合力学性能起到决定性的作用。在740℃采用0.25%Al-3B变质处理后,铸造Al-10Si合金的抗拉强度和延伸率分别提高了11.7%和86.3%,该合金综合力学性能得到大幅提高。

Al-3B Modification on Microstructure and Mechanical Properties of Al-10Si Alloy

Under general casting conditions,the microstructure of hypoeutectic Al-Si alloy consisted of coarse dendrite primaryα-Al phase and eutectic structure.The coarse primaryα-Al phase reduced the strength and hardness of hypoeutectic Al-Si alloy,and the needle like eutectic silicon splited the matrix and easily initiated cracks,which affected the improvement of elongation and toughness of hypoeutectic Al-Si alloy.Therefore,refining dendrite primaryα-Al phase and improving the morphology of eutectic silicon will effectively improve the mechanical properties of hypoeutectic Al-Si alloy.The modification of Al-10 Si alloy by Al-3B and the effect of Al-3B on the volume fraction of primaryα-Al phase were mainly studied in this paper,and the phenomenon was explained by the movement of eutectic point and leverage law.The research results had important reference value for broadening the application field of hypoeutectic Al-Si alloy.Al-10 i alloy was melted at 740℃,and then modified with 0,0.10%,0.25%,0.40%,0.55%and 0.70%(mass fraction)Al-3B,respectively.The effect of modifier content on microstructure and mechanical properties of Al-10 Si alloy was studied.In order to study the effect of modification temperature on microstructure and mechanical properties,Al-10 Si alloy was prepared at 700,740 and 780℃,respectively,and modified with 0.25%Al-3B.After 3 min of modification,the alloy solution was poured into the metal mold with the inner cavity size ofΦ12 mm×100 mm to obtain the alloy sample.The microstructure of the alloy was observed and analyzed by optical microscope(OM).The mechanical properties of the alloy were tested by universal electronic testing machine.The tensile fracture morphology of the alloy before and after modification was observed by scanning electron microscope(SEM),and the cooling curve of the alloy was measured by differential scanning calorimeter(DSC).The results showed that the solidification super-cooling degree of Al-10 Si alloy decreased after modification with Al-3B.When the modification temperature was constant,the volume fraction of primaryα-Al phase in Al-10 Si alloy increased first and then decreased with the increase of content of Al-3B.When the content of Al-3B was 0.25%,the volume fraction of the primaryα-Al reached the maximum value of 42.8%,and the Si phase existed in the form of small short plate or short rod.With the same content of Al-3B,when the modification temperature increased from 700 to 740℃,the cooling rate of Al-Si alloy increased with the increase of temperature,which made the undercooling degree of hypereutectic Al-Si alloy increased more,and the non-equilibrium eutectic point moved more to the right.When the modification temperature increased from740 to 780℃,the cooling rate of Al-Si alloy liquid decreased,resulting in less increase of undercooling degree of alloy liquid and less movement of non-equilibrium eutectic point to the right.With the increase of Al-3B content,the tensile strength and elongation of Al-10 Si alloy increased first and then decreased.When the content of Al-3B was 0.25%,the tensile strength and elongation of Al-10 Si alloy reached the maximum value.The effect of Al-3B modifier content on the tensile strength and elongation of Al-10 Si alloy was consistent with its effect on the volume fraction of primaryα-Al phase in the alloy.The volume fraction of primaryα-Al phase,the size and morphology of eutectic Si played a decisive role in the comprehensive mechanical properties of the alloy.In addition,the size and morphology of Si phase in the modified alloy played a key role in the tensile strength,especially the elongation of the alloy.Compared with the unmodified Al-10 Si alloy,the tensile strength and elongation of 0.25%Al-3B modified Al-10 i alloy increased by 11.7%and86.3%,respectively.The results showed that modification of cast Al-10 Si alloy with Al-3B was beneficial to refine dendrite primaryα-Al phase and improve the morphology of eutectic silicon,which greatly improved the tensile strength and elongation of cast Al-10 Si alloy.