過共晶鋁矽合金之高溫硬度與耐磨耗性質

High Temperature Hardness and Wear Resistance in Hypereutectic Al-Si Alloys

江承祖(Chen-chu Chiang)

指導教授 ： 楊智富

大同大學/工程學院/材料工程學系所/碩士(2011年)

摘要

本研究探討五種過共晶鋁矽合金之高溫硬度與耐磨耗性質，包括A390 (細化)、BH390(未細化)、BH390(細化)、BH390 + 5% Si(細化)及BH390(汽缸)。藉由光學顯微鏡（OM）、掃描式電子顯微鏡（SEM）、成分分析儀（分光儀）、電子微探儀（EPMA）、微式硬度儀(HV)、洛氏硬度儀(HRB)、原子力學顯微鏡 (AFM)，以及根據ASTM G-133進行線性式往復磨擦試驗，來探討五種過共晶鋁矽合金之室溫及高溫機械性質。
微硬度試驗結果顯示，合金經T5時效處理後，共晶組織之硬度皆呈現上升之趨勢，其中BH390合金硬度皆略優於A390合金，乃因BH390合金有較佳之析出強化。室溫HRB硬度量測結果同樣顯示BH390(含有略高含量之Mg及Zr)較A390有較佳之硬度；另外，BH390+ 5% Si(細化)之室溫HRB硬度與BH390者相近。高溫HRB硬度量測顯示，BH390 + 5% Si(細化)為高溫下硬度最高者。顯示較多矽顆粒可提升合金之高溫硬度。
磨耗試驗結果顯示，BH390(汽缸)為室溫乾式磨耗下最為耐磨耗者，此乃因BH390(汽缸)有壓力鑄造之製程細化處理，及化學細化處理之雙重效果，使初晶矽非常細小(d=18μm)，於室溫磨耗試驗下具最佳之抗磨耗性；而BH390 + 5% Si(細化)合金為高溫乾式磨耗試驗下為最耐磨耗者，乃因高溫環境下因共晶基地相對柔軟，無法支撐初晶矽，但若有較多且細小分布均勻之矽顆粒，對抗磨耗性質有很大的幫助；BH390(細化)合金經矽浮出之鹼洗後，不論於室溫或高溫磨耗條件下，其耐磨耗性質皆優於未經矽浮出前之鋁矽合金，因矽顆粒經鹼洗後呈島狀浮出於共晶組織上，於磨耗前期階段能有效支撐負載，可降低磨耗損失量，若於試驗中添加潤滑油，除能延緩或降低磨耗外，經由磨頭之往復運動，潤滑油將被帶動並填充島狀初晶矽與基地間之落差，形成一連續性湖泊，降低磨頭與合金之直接接觸，進而改善合金之抗磨耗性，可降低磨耗量。

關鍵字

鋁矽合金 ； 耐磨耗 ； 機械性質

並列摘要

Microstructures and elevated temperature hardness and wear behaviors in five hyper-eutectic Al-Si alloys, namely A390 (modified), BH390 (un-modified), BH390 (modified), BH390 + 5% Si (modified) and BH390 (die cast cylinder), are investigated in this study by using OM, SEM, GDOS, EPMA, HV, HRB and AFM. The wear tests were performed in a linearly reciprocating ball-on-plate sliding wear test apparatus in accordance to ASTM G-133 specifications.
Micro-hardness in the eutectic micro-constituents of these Al-Si alloys showed an increase by a T5 heat treatment. It was also shown that the eutectic micro-constituents in BH390 alloys (having slightly higher Mg and Zr contents than that of A390 alloy) are harder than that of A390 alloy. The room temperature HRB hardness test results also showed the BH390 alloys to be harder than the A390 alloy. It was noticed that the room temperature HRB hardness of the BH390 + 5%Si alloy (modified) is very close to that of the BH390 alloys. On the other hand, the high temperature hardness test (at 225oC) showed that the HRB hardness of the BH390 + 5%Si alloy (modified) is higher than the rest of Al-Si alloys. This indicates that the greater amount of primary Si particles in the BH390 + 5%Si alloy (modified) can effectively enhance its high temperature hardness.
The room temperature wear test results showed that the BH390 (die cast cylinder) to be the highest wear resistant alloy among the Al-Si alloys. The reason of that lies in the fact that the BH390 (die cast cylinder) specimen was chemically modified and chill casted (pressure die cast) to results in a microstructure with very fine primary Si particles (d≦18 μm) to resist wear from happening. As for high temperature wear test (at 225oC), the BH390 + 5%Si alloy (modified), having a greater amount of primary Si particles, exhibits the highest wear resistance among the Al-Si alloys.
When subjected to an etching treatment (using 10% NaOH for 45 s) the primary Si particles are exposed as islands above the eutectic micro-constituents matrix for about 0.3~0.5 μm in height. Since these exposed Si particles can effectively reduce the wear loss of the relatively softer eutectic micro-constituents matrix, the etched Al-Si alloys therefore exhibited improved wear resistance than those un-etched under test conditions at both room and elevated temperatures and with or without lubricant.

並列關鍵字

Al-Si alloys ； wear resistance ； hardness

參考文獻

[4] Fareg Saeid, Moftah Saeid, “Effect of Material Structure Machining characteristics of Hypereutectic Al-Si Alloy”, Mechanical - Advanced Manufacturing Technology, 2007.

[7] P. R. Rios, G.S.Fonseca, “Grain Boundary Pinning by Al6Mn Precipitates in an Al-1wt% Mn Alloy”, Scripta Materialia, 50, pp.71-75, 2004.

[8] X.D.Du, “Study on Ageing and Creep of Al–0.1Zr Alloy , Materials Science and Engineering”, A432, pp.84-89, 2006.

[9] J.D.Robson, “A New Model for Prediction of Dispersoid Precipitation in Aluminium Alloys Containing Zirconium and Scandium”, Acta Materialia, 52, pp.1409-1421, 2004.

[12] 蘇彥豪，汽車引擎用噴覆成型高矽鋁合金汽缸套之開發，國立成功大學博士論文，頁3-6、頁10-15、頁51-53，2004。