【作者】 钱钊；

【导师】 刘相法；

【作者基本信息】 山东大学 ， 材料加工工程， 2009， 硕士

【摘要】 为提高Al-Si多元活塞合金的高温强度,本文采用铸造合金化的方法在工业试验条件下研究了Mn、RE、Ni、Fe等几种微合金化、合金化元素对Al-Si多元活塞合金的高温强化效果,并探索了挤压铸造对活塞合金力学性能的影响。利用扫描电镜（SEM）、光学显微镜（OM）、电子探针（EPMA）、X射线衍射仪（XRD）、差式扫描量热仪（DSC）等手段,分析了所制备各合金的微观组织、相组成与种类及一些合金的凝固过程,并对各活塞合金的高温强化机理进行了探讨。分别研究了微量Mn元素和微量混合RE对ZL109活塞合金的高温强化效果。发现随着合金中Mn含量的增加,ZL109合金中会出现含Mn化合相的演变。其中,加入的微量Mn元素当大多数存在于树枝状的Al₉FeNi耐热相中时其具有最佳的高温强化效果,再进一步增加Mn含量会导致形态很差的一种板片状含Mn相生成,使高温强化效果变差。研究发现微量混合RE也可对Al-Si多元活塞合金起到微合金化作用,明显提高合金的高温抗拉强度。微量富铈混合RE的加入可使得合金中AlNiCu耐热相的数量增多,体积分数增大,从而起到热强化效用。此外,混合RE的加入还可在合金中形成一种新的颗粒状富RE化合相。探索了挤压铸造方法对Al-Si多元活塞合金力学性能与显微组织的影响。试验发现挤压铸造可明显提高活塞合金的室温力学性能,但对高温抗拉强度的提高作用不大,与重力铸造相比甚至降低合金的高温抗拉强度。挤压铸造可使合金中的共晶Si呈粗棒或块状分布,而不再呈重力铸造合金中典型的针片状,从而降低了其割裂α-Al基体的不利影响。此外还发现,挤压铸造易促使活塞合金中的Al₉FeNi化合相呈粗大状析出,对合金的高温强度造成不利影响。在A牌号高性能活塞合金的基础上进行了Ni元素的进一步强化探索。试验发现,随着合金中Ni含量的增加,合金组织中的主要耐热相发生演变:从网状的Al₃CuNi演变为环絮状且呈封闭或半封闭态分布在α-Al枝晶晶界上的Al₉FeNi,最后演变为呈粗骨状的Al₉FeNi。其中,当Al₉FeNi呈环絮状封闭或半封闭分布在α-Al枝晶晶界上时,合金的高温强度有最显著的提高,且室温、高温综合强度最好。为尽量节省昂贵元素尤其是Ni在高性能活塞合金中的使用,制备了Fe、Cu、Ni综合强化的高强耐热活塞合金。试验发现Fe的适量加入可在活塞合金中形成形态较好的块状Al₉FeNi耐热相,对提高合金的高温强度尤其是350℃以上的高温抗拉强度有利;但添加过多的Fe则会导致合金中生成形态很差的粗大Al₉FeNi相。此外,在利用Fe、Cu、Ni综合强化时辅助加入Cr元素可进一步强化活塞合金。Cr的加入可使合金中生成热稳定性非常高的Al₁₅（Fe,Cr,Mn）₃Si₂耐热相,它与其它热强相如Al₉FeNi、Al₃CuNi、Al₇Cu₄Ni等一起可起到高温下共同强化α-Al基体的作用,从而使合金的高温强度大幅度提高,其中350℃时的抗拉强度可高达99.77MPa。更多还原

【Abstract】 The elevated temperature strengthening effects of several trace-alloying and alloying elements such as Mn,RE,Ni,Fe on Al-Si piston alloys and the influence of squeeze casting on the mechanical properties of piston alloys have been investigated for the purpose of increasing the elevated temperature strengths of industrial aluminium-silicon piston alloys.By means of SEM,OM,EPMA,XRD and DSC,the microstructures,phase compositions and phase types of the prepared alloys and the solidification of some piston alloys are analyzed in this thesis,which helps to discuss the strengthening mechanism of piston alloys at elevated temperatures.The high temperature strengthening effects of trace Mn and RE have been studied respectively.It has been found that there occurs an evolution of Mn-bearing intermetallic phases in ZL109 piston alloy as the Mn content increases in the alloy. When most of manganese exists in the dendritic Al₉FeNi phase,the elevated temperature strengthening effect is good.Further increase of Mn addition can lead to the formation of a kind of plate-like Mn-bearing phase,whose strengthening effect is poor.It is found that trace RE addition can also play an effective role in strengthening Al-Si piston alloy at elevated temperatures.The addition of trace RE into the alloy can increase the volume fraction of the heat-resistant AlNiCu compound in ZL109 alloy.In addition,a kind of nodular RE-rich intermetallic phase is formed in the alloy after addition of RE.The influences of squeeze casting on the mechanical properties and microstructures of Al-Si piston alloys were also evaluated.It is found by experiments that the squeeze casting can improve the mechanical properties of Al-Si piston alloys evidently at room temperature but reduce the ultimate tensile strength（UTS） at elevated temperatures.The eutectic silicon in the squeeze cast Al-Si piston alloy characterizes as short-rod shaped instead of needle-like in gravity die casting Al-Si piston alloys.This helps to weaken the harmful effect of needle-like eutectic silicon on the alloy.It is also found that the squeeze casting can promote the formation of Al₉FeNi phase with coarse sizes,which may be the reason for the decrease of tensile strength at elevated temperatures.The investigation of potential strengthening effects of Ni on a high-performance piston alloy was conducted.It has been found that with the increase of Ni content, there occurs an evolution of main heat-resistant compounds in alloys:from the net-like Al₃CuNi to the Al₉FeNi phase distributing inα-Al dendrites boundaries with the shape of closed or semi-closed vermicule,and then to the Al₉FeNi phase like coarse bones.Among them,the vermicular Al₉FeNi phase distributing inα-Al dendrites boundaries has the most evident elevated temperature strengthening effect on the piston alloy.For the purpose of decreasing the use of the expensive element Ni in high-performance piston alloys as possible as it can,the new heat-resistant Al-Si piston alloys strengthened synthetically by Fe,Cu and Ni were fabricated and investigated.It is found that the proper addition of iron into the alloy helps to form the blocky Al₉FeNi heat-resistant phase,which can increase the UTS of piston alloys at elevated temperatures especially when above 350℃;but the excessive amount of Fe addition will lead to the formation of very coarse Al₉FeNi with had morphologies. Based on the above research,the addition of element Cr into the alloy was also tried combining with Fe,Cu and Ni.The result has shown that it helps to further strengthen the alloy.It is found that Cr can form the Al₁₅（Fe,Cr,Mn）₃Si₂ phase,which is a kind of heat-resistant intermetallic compound with a very high thermal stability.Jointly with other heat-resistant phases such as Al₉FeNi,Al₃CuNi and Al₇Cu₄Ni in alloy,the Al₁₅（Fe,Cr,Mn）₃Si₂ compound can play important roles in strengtheningα-Al matrix at elevated temperatures,which results in the increase of ultimate tensile strength of the alloy:the value can reach up to 99.77MPa at 350℃.更多还原