On the observation of a new ternary MgSiCa phase in Mg-Si alloys
On the observation of a new ternary MgSiCa phase in Mg-Si alloys
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DOI：
10.1007/s11661-998-0099-9
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发表时间：
1998-06
期刊：
影响因子：
--
通讯作者：
Y. Carbonneau;A. Couture;A. Neste;R. Tremblay
中科院分区：
文献类型：
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作者：
Y. Carbonneau;A. Couture;A. Neste;R. Tremblay
汽车工业正年复一年地成为镁基合金等轻质材料开发和应用的优势领域。['Jj 镁合金在该行业的使用（特别是以压铸件的形式）不断增加，预计到 2000 年每辆汽车的平均重量将超过 40 公斤 [2] 事实上，汽车工业正在使用 70% 的镁压铸件。 美国 大多数时候，镁合金（主要是AZ91D）仅限于工作温度低于120 oC的结构应用，因为它们缺乏足够的抗蠕变性。尽管一些镁合金在高温下具有更好的抗蠕变性，但它们与昂贵的元素如锆、银、钇、钍和稀土元素形成合金。这些昂贵合金的使用仅限于高性能发动机，例如一级方程式赛车、飞机和导弹。['>'5] 例如，合金 WE54 通常用作赛车发动机中的活塞材料，并且抗蠕变温度高达 300 oC。[61 这种情况为开发低成本、抗蠕变镁基合金打开了大门，用于更多领域的“引擎盖下”应用。 传统汽车。在这方面，Mg-Si 二元系统显示出作为活塞材料的特殊潜力，这主要是由于这些合金中存在金属间相 Mg2Si。这种立方面心金属间化合物具有高熔点（1085 oC）、高硬度（460 HVo3）、低密度（1.9 g/cm3）和低热膨胀系数（7.5 x 10 6 K 1）。[16]二元 Mg-Si 相图如图 1 所示。由于与基体中存在的 Mg2Si 金属间相的枝晶形态相关的问题，镁硅合金已被搁置很长一段时间。这种形态会损害合金的铸造性和最终机械性能。为了克服这个缺点，人们进行了许多尝试来修改这种特定的形态。通过机械变形或化学添加获得了一些成果。[ib'I8 Carbonneau 等人。 l291通过添加少量的Ca，成功地将Mg-2 pct Si和Mg-4 pct Si合金中的Mg2Si树枝晶形态分解成细小且分布均匀的圆形颗粒。大多数抗蠕变合金依赖于镁基体中精细分布的金属间相的沉淀。这些细小析出物改善抗蠕变性能的效率在很大程度上与其热稳定性有关。这种热稳定性与扩散现象有关，与沉淀物的熔化温度成正比。在这方面，由于金属间化合物 Mg2Si 的熔化温度高，Mg-Si 合金具有很高的抗蠕变潜力。最接近的含 Mg 的高熔点金属间化合物是在合金 WE54（780 oC 下的 Mg2Y）中发现的。["]Carbonneau 等人最近对 Ca 改性 Mg-Si 系统的研究[29] 观察到了一种新的三元相，称为 Mg-Si-Ca。每当 Ca 重量增加时，这种三元相就会出现在 Mg-2 pct Si 和 Mg-4 pct Si 合金中。 分数大于0.8%。据我们所知，镁合金中从未报道过这种三元相的出现。铸造实验合金的化学分析是通过小冷却试样（12 毫米厚，直径 42 毫米）的感应耦合等离子体进行的。铸造合金的化学成分见表 I。描述了实验熔化、合金化和铸造程序 其他地方。[2930 使用尼康进行金相观察和定量金相学......
The automotive industry is becoming, year after year, a privileged scene for the development and application of light materials such as Mg-based alloys.['Jj The use of Mg alloys in this sector (particularly in the form of die castings) has been increasing constantly and is expected to reach an average weight of more than 40 kg per automobile by the year 2000 [2] In fact, the automotive industry is using 70 pct of all Mg die castings produced in the United States Most of the time, Mg alloys (mainly AZ91D) are limited to structural applications with operating temperatures lower than 120 oC because they lack a sufficient creep resistance. Although some Mg alloys presenting better creep resistance at elevated temperature are available, they are alloyed with costly elements such as Zr, Ag, Y, Th, and rare earths. The use of these expensive alloys is restricted to high-performance engines such as in Formula 1 race cars, airplanes, and missiles.['>'5] For example, the alloy WE54 is commonly used as a piston material in race car engines and is creep resistant up to 300 oC.[61 This situation opens the door for the development of a low cost, creep resistant Mg-based alloy for" under-the-hood" applications in more conventional automobiles. In this regard, the Mg-Si binary system shows an exceptional potential as a piston material due principally to the intermetallic phase Mg2Si present in those alloys. This cubic face centered intermetallic possesses a high melting point (1085 oC), high hardness (460 HVo3), low density (1.9 g/cm3), and low thermal expansion coefficient (7.5 x 10 6 K 1).[16] The binary Mg-Si phase diagram is presented in Figure 1. Magnesium-silicon alloys have been put aside for a long period of time because of problems associated with the dendritic morphology of the Mg2Si intermetallic phase present in the matrix. This morphology impairs both the castability and the final mechanical properties of the alloy. To overcome this drawback, many attempts were made to modify this particular morphology. Some achievements were obtained by mechanical deformation or by chemical additions.[ib'I8 Carbonneau et al. l291 succeeded in breaking down the dendritic morphology of Mg2Si present in Mg-2 pct Si and Mg-4 pct Si alloys into small and well-distributed round particles by adding small amounts of Ca. Most creep resistant alloys rely on the precipitation of a finely distributed intermetallic phase in the Mg matrix. The efficiency of these fine precipitates in improving the creep resistance is related to a great extent to their thermal stability. This thermal stability, being connected to diffusion phenomena, is proportional to the melting temperature of the precipitates. In this regard, Mg-Si alloys present a high potential for creep resistance due to the high melting temperature of the intermetallic, Mg2Si. The closest high melting point intermetallic containing Mg is found in alloy WE54 (Mg2Y at 780 oC).["]Recent work by Carbonneau et al.[29] on the Ca-modified Mg-Si system has led to the observation of a new ternary phase identified as Mg-Si-Ca. This ternary phase is present in Mg-2 pct Si and Mg-4 pct Si alloys whenever the Ca weight fraction is greater than 0.8 pct. To our knowledge, the occurrence of this ternary phase has never before been reported in Mg alloys. Chemical analysis of the cast experimental alloys was performed by inductively coupled plasma from small chilled coupons (12-mm thick by 42 mm in diameter). The chemical composition of the cast alloys appears in Table I. The experimental melting, alloying, and casting procedures are described elsewhere.[2930 Metallographic observations and quantitative metallography were performed using a Nikon …