重力铸造Mg-5.8Sm-0.4Zn-0.3Zr合金的热处理研究

重力铸造制备了Mg-5.8Sm-0.4Zn-0.3Zr(SZ58K)镁合金,对其进行固溶处理,并绘制了时效曲线。采用X射线衍射分析(XRD)、光学金相分析(OM)、扫描电子显微分析(SEM)等手段,研究了热处理(固溶处理、时效处理)对SZ58K镁合金的显微组织和力学性能的影响。结果表明,合金的铸态组织由α-Mg基体和晶界附近的Mg41Sm5相组成;固溶处理后,第二相组织分解,晶体内部出现少量小尺寸方块状相,其主要成分为Sm;晶粒尺寸略微长大,抗拉强度和塑性大幅提高,但屈服强度无明显变化;再经过时效处理(T6)后,屈服强度大幅提高,但由于塑性剧烈下降,抗拉强度提高幅度较小。     

大配缸间隙活塞外圆型线对发动机NVH性能的影响

为降低冷起动时大配缸间隙活塞的噪声,提高其噪声、振动、声振粗糙度(noise vibration harshness, NVH)性能,应用活塞动态分析软件PIMO3D,建立活塞弹性流体动力学模型,计算分析冷起动状态下大配缸间隙的活塞外圆型线对NVH性能的影响。分析结果表明：噪声主要产生在做功冲程初始阶段(上止点后曲轴转角为20°～60°),产生原因为活塞换向导致主推力侧裙部上端对缸套的拍击;NVH性能与主推力侧裙部下端接触点到裙部上端敲击点的高度差有关,敲击点越靠近活塞最大外圆位置,撞击产生的振动速度级越小。重新设计活塞裙部基础型线,在型线最大外圆的上、下方各增加一个凹面,形成双凹面型线。仿真验证结果表明：双凹面型线可以有效控制活塞裙部与缸套接触点的位置及接触点的落差,降低大配缸间隙活塞的噪声。     

HRTEM studies of aging precipitate phases in the Mg-10Gd-3Y-0.4Zr alloy

Rare-earth(RE) element addition can remarkably improve the mechanical properties of magnesium alloys through precipitation hardening. The morphology, distribution and crystal structure of precipitates are regarded as major strengthening mechanisms in the Mg-RE alloys. In order to understand the formation of precipitates during aging at 225 oC in a Mg-10Gd-3Y-0.4Zr alloy(GW103K) with high strength and heat resistance, a high-resolution transmission electron microscopy(HRTEM) was employed to characterize the microstructural evolution. It was found that three types of precipitates were observed in the alloy at the early stage, named as: single layer D019 structure, one single layer D019 structure and one layer of Mg, two parallel single layers(containing RE) and Mg layer in between, which was regarded as ordered segregation of RE, precursors to form β′′ and β′ phase, respectively. Both of β′′ and β′ phase were transformed from the precursors. It was also found that large size of β′ phase and the small size of β′′ phase were constantly existent in the whole aging process. β′ phase played a major role in the strengthening of the GW103 K alloys and the decrease of the hardness was caused by the coarsening of β′ phase.     

低温形变热处理制备Mg-6Gd-1Y-0.5Zr合金的力学性能(英文)

对固溶态的Mg-6Gd-1Y-0.5Zr合金进行低温形变热处理,处理工艺包括不同应变量的冷拉伸和随后在200°C进行的峰值时效。结果表明:低温形变热处理合金的时效硬化动力学显著加速,随变形量增大,合金的峰值时效时间大幅度缩短。冷拉伸变形量为10%的合金在200°C峰值时效后的屈服强度、抗拉强度和伸长率分别达到251MPa、296MPa和8%,这些性能大大超过传统商业牌号的耐热镁合金WE54,尽管其总的稀土含量高于GW61K合金。