AlN变质对Al-4Si-0.45Mg合金性能的影响

Effects of AlN Modification on Properties of Al-4Si-0.45Mg Alloy

在亚共晶Al-4Si-0.45Mg合金中添加微量AlN,以改善合金的显微组织并提高其力学性能和导热性能。结果表明,未添加Sr和AlN的合金,其抗拉强度为167.3 MPa,伸长率为10%,热导率为149.5 W/(m·K);添加Sr后的抗拉强度为176.2 MPa,伸长率为20%,热导率为166.8 W/(m·K),抗拉强度和热导率分别提高了5.4%、11.6%;添加AlN后的合金抗拉强度为194.8 MPa,伸长率为16%,热导率为170.1 W/(m·K),抗拉强度和热导率分别提高了16.4%、13.8%。力学性能的提高主要与α-Al的晶粒细化、二次枝晶臂间距(SADS)的减小和Si的变质有关。加入Sr和AlN后,共晶Si由片状变成块状和球状,Sr变质后共晶Si的尺寸明显减少,且AlN变质后共晶Si的平均尺寸更小,说明热导率的提高主要与共晶Si相的形态变化有关。其机制为细小的Si使得电子通道增加,电子散射概率降低,平均自由程增加,从而提高了热导率。

Trace AlN was added to the hypoeutectic Al-4Si-0.45Mg alloy to modify the microstructure and improve the mechanical properties and thermal conductivity. The results indicate that the tensile strength, elongation and thermal conductivity of the alloy before Sr and AlN addition reach 167.3 MPa, 10%, and 149.5 W/(m·K), respectively. After Sr addition, the tensile strength and elongation reach 176.2 MPa and 20%, which are enhanced by 5.4% and 11.6%, respectively, and thermal conductivity is 166.8 W/(m·K). After AlN addition, the tensile strength and elongation of the alloy reach 194.8 MPa and 16%, which are enhanced by 16.4% and 13.8%, respectively, and thermal conductivity is 170.1 W/(m·K). The improvement of mechanical properties is mainly related to the α-Al grain refinement, the reduction of secondary dendrite arm spacing(SADS) and Si modification. After adding Sr and AlN, the eutectic silicon is transformed from flake to block and spherical. The dimension of eutectic Si after modification is significantly reduced, and the average size of the eutectic Si after the AlN modification is smaller, indicating that the increase of coefficient is mainly related to the morphology evolution of eutectic Si phase. The mechanism is that the electron channel is increased by fine Si, leading to decrease of electron scattering probability and increase of mean free path, thereby improving the thermal conductivity.