Sains Malaysiana 37(2): 189-193(2008)

Pengaruh Unsur Zirkonium Terhadap Sifat Mekanik

Aloi Tempaan Al-1.2Si-0.5Mg-0.25Fe

(Influence of Zirconium on Mechanical Properties of

 Al-1.2Si-0.5Mg-0.25 Fe Wrought Alloy)

Karen Wong Mee Chu, Abdul Razak Daud & Azman Jalar

Pusat Pengajian Fizik Gunaan, Fakulti Sains & Teknologi

Universiti Kebangsaan Malaysia,43600 Bangi,

Selangor Darul Ehsan, Malaysia

Diserahkan:  17 Mei 2007 / Diterima:  28 Ogos 2007

ABSTRAK

Aloi aluminium tempaan terawat haba siri 6XXX perlu melalui pelbagai proses termomekanik sebelum sedia digunakan sebagai badan luar kereta. Penuaan tabii yang lama pada suhu bilik memberi kesan yang tidak baik terhadap pengerasan tuaan. Ramai pengkaji telah memperkenalkan langkah tambahan seperti pra-penuaan untuk mengatasi masalah tersebut. Kajian ini bertujuan untuk meningkatkan respons pengerasan tuaan aloi Al-1.2Si-0.5Mg-0.25Fe berbentuk kepingan melalui penambahan Zr antara 0.02 hingga 0.30% bt. Aloi yang dikaji dilindap kejut air ke suhu bilik dan dibiarkan mengalami penuaan tabii selama 14 hari sebelum rawatan haba pada suhu 180ºC selama 30 minit dan juga 11 jam. Mikrokekerasan aloi Al-1.2Si-0.5Mg-0.25Fe tanpa Zr ialah 80.2 VHN untuk rawatan haba 30 minit dan 105.0 VHN untuk rawatan haba 11 jam. Mikrokekerasan, kekuatan tegangan dan kekuatan alah aloi yang mengandungi Zr dan dirawat haba pada 180ºC selama 11 jam adalah jauh lebih tinggi berbanding dengan set aloi yang sama tetapi dirawat haba selama 30 minit. Namun begitu, aloi yang mengandungi 0.30% bt. Zr dan dirawat haba selama 30 minit mempunyai mikrokekerasan, kekuatan tegangan dan kekuatan alah yang lebih tinggi daripada aloi tanpa Zr tetapi dirawat haba selama 11 jam. Peningkatan sifat mekanik yang dilaporkan dikaitkan dengan fenomena penghalusan butiran.

Kata kunci: mikrokekerasan; kekuatan tegangan muktamad; kekuatan alah; penghalusan butiran

ABSTRACT

The heat-treatable 6XXX series wrought aluminium alloys need to undergo various thermomechanical processes before they can be used as external car body skin. A lengthy natural aging at room temperature is detrimental to the age hardening of these alloys. Many researchers introduced an additional step such as pre-aging to offset the detrimental effects of the natural aging. The present work is aimed to improve the age-hardening response of the Al-1.2Si-0.5Mg-0.25Fe sheet alloy through Zr additions between 0.02 to 0.30 wt.%. The alloys were water-quenched to room temperature and naturally aged for 14 days before undergoing heat-treatment at 180ºC for 30 minutes and 11 hours.Microhardness of Al-1.2Si-0.5Mg-0.25Fe alloy without Zr is 80.2 VHN for the 30 minutes heat-treatment and 105.0 VHN for the 11 hours heat-treatment. Microhardness, ultimate tensile strength and yield strength values for alloys containing Zr heat-treated at 180ºC for 11 hours are far more superior compared to the same set of alloys heat-treated for 30 minutes. Nevertheless, alloy containing 0.30 wt.% Zr which was heat-treated for 30 minutes have higher microhardness, ultimate tensile strength and yield strength compared to the alloy without Zr which was heat-treated for 11 hours. Increment in the mechanical properties reported is attributed to grain refinemen phenomenon.

Keywords:  microhardness; ultimate tensile strength; yield strength; grain refinement

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