【作者】 强旭东；

【导师】 阎峰云；

【作者基本信息】 兰州理工大学 ， 材料加工工程， 2008， 硕士

【摘要】 目前镁合金半固态成形技术研究所用合金成分均在第二组元的固溶度极限范围内,亦即沿用传统商业牌号的合金。论文突破传统,大胆选择亚共晶范围内的镁铝合金进行半固态触变压铸的研究和探索。这样,首先面临的问题是如何制备适于半固态加工的合金坯料,半固态等温热处理法将非枝晶组织坯料的制备与二次加热合并为一个步骤,其中前期的锭料熔铸、半固态坯料制备等工艺过程控制是决定半固态触变压铸成败的关键。因此,本部分选择了含铝量分别为15%,20%,25%三种不同成分的镁合金,对其等温热处理过程的组织演变做了系统研究,前期的初步试验证明了此方案的可行性。最终得到具有触变性的半固态非枝晶组织。论文通过等温处理法制备半固态坯料,研究了含铝20%和15%镁合金半固态触变压铸的工艺特点及对组织、力学性能的影响。采用自行设计的压铸机加热式压室改变了传统压铸机不能用于半固态压铸的状况,加热的压室补充了合金液所散失的热量,减缓了合金溶液在压室中凝固的速度,保证金属有较好的流动性,以满足半固态镁合金压铸成形的要求。实验中考察压射速度、压射比压和模具温度三个工艺参数对压铸件力学性能和组织的影响,把其中两个参数固定在较佳值,考察第三个参数的影响。对于20%合金,在压射比压40MPa,压射速度4 m/s,模具温度160℃时其力学性能最佳,抗拉强度为220MPa,伸长率为5.63%,硬度值98.5HB,冲击韧性8.53J/cm~2。在对半固态压铸零件进行T4处理后,其力学性能均有所提高,其抗拉强度达到了238MPa,伸长率达到了6.71%。触变压铸成形后的组织比等温处理后更加均匀、细小。通过对半固态成形试棒拉伸断口形貌分析,发现半固态成形拉伸试棒的断裂方式主要为沿晶断裂。为了便于比较,通过正交实验,研究了15%合金的液态压铸工艺。研究结果表明,压铸工艺参数对15%镁合金力学性能影响的显著性。对抗拉强度的影响由大到小依次为:压射速度、模具温度、浇注温度、压射比压;延伸率依次为:浇注温度、模具温度、压射速度、压射比压。15%镁合金压铸工艺最优方案为:浇注温度为650℃,模具温度为150℃,压射速度为3.5m/s,压射比压为75MPa。对于20%合金液态压铸,平均抗拉强度190MPa,平均延伸率3.19%。通过扫描电镜观察拉伸断口,发现断口存在较多的气孔和疏松,15%压铸镁合金的断裂方式为解理断裂。更多还原

【Abstract】 At present the application of magnesium alloy components in the solution are within the limitation of Solid solubility, the dissertation has breakthrough of tradition with choosing Hypo-eutectic scope, using AZ91D method for the transformation boldy. It is a difficult point to how to prepare suitable for the processing of semi-solid alloy magnesium alloy billets. This way makes semi-solid isothermal treatment of non-dendritic structure blank Preparation and reheating the merger become a step, but preparation and control blank is inevitable. Therefore, the choice of the aluminium are respective 15%, 20%, 25%, these three different ingredients of magnesium alloy. which has been done more group testing, the initial pre-trial proved the feasibility of this option. Finally, getting a structure of semi-solid non-dendritic with Thixotropy .This paper in with of prepares semi-solid billets through the isothermal treatment, which has studied the aluminiferous 20% and 15% magnesium alloy semi-solid process characteristics Thixo-casting .The tradition chamber can not been used in semi-solid diecasting, now, the condition has changed, because the chamber which designed for semi-solid diecasting was used in the experience. The heated chamber can keeps the semi-solid alloy in higher temperature and delays the freezing speed. The excellent fluidity of the alloy fit the semi-solid diecasting of magnesium alloy. The influences of filling speed and pressure of die-casting and mold temperature was investigated to mechanical properties and organization’s influence of alloy.Two parameters fixes in the good parameter,studys influence of the third parameter. The result indicated that mechanical properties of the best when injection pressure of 40 MPa, injection speed of 4 m/s, mold temperature at 160℃.The tensile strength has the maximal of 220MPa and the elongation is 5.63% and hardness is 98.5HB and impact toughness is 8.53J/cm~2.After T4 treatment, the tensile strength increased to 238MPa, elongation is 6.71%. Thixocasting forming the organization more evenly distributed.The fracture morphology of tensile tested specimens has analysed. The result indicated that the fracture morphology of the semi-solid diecasting was along grain boundaries mainly.For purposes of comparison, by orthogonal experiments on 15% of the liquid alloy die-casting process.The results show that the factors influencing on properties of 15% from the greatest to the smallest are following: on tensile strength are injection speed, mould temperature, pouring temperature and injection pressure; on elongation are pouring temperature, mould temperature, injection speed and injection pressure. In the experiment, the mechanical properties of 15% magnesium alloy were obtain preferable value, at the proper factors: pouring temperature is 650℃, mould temperature is 150℃, injection speed is 3.5m/s, injection pressure is 75MPa. For 20% of liquid alloy die-casting, the average tensile strength of 190 MPa, the average rate of 3.19% extension. We can observe carefully the break surface by means of SEM, the fracture morphology of tensile tested 15% magnesium alloy is cleavage fracture, and pull break surface as same as impact break surface. There are many porosities and different crack.更多还原