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Hot tearing susceptibility of AA3000 aluminum alloy containing Cu, Ti, and Zr
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.ORCID iD: 0000-0002-3622-4247
2019 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 50A, no 8, p. 3842-3854Article in journal (Refereed) Published
Abstract [en]

Severe hot tearing has been observed during DC casting of modified AA3000 alloys with additions of Cu, Ti, and Zr, although these alloys are regarded as rather easy to cast. Extensive studies have been performed on both synthetic and industrial AA2000, AA6000, and AA7000 alloys, but less data are available for AA3000 alloys. This work was thus initiated to investigate the hot tearing susceptibility of AA3000 alloys with varying alloy element content using constrained rod casting molds. The results showed that the Cu and Fe content have a major impact on hot tearing resistance, while the effects of Zr and Ti are minor. Cu in a range from 0.3 to 1.2 wt pct significantly increased the hot tearing tendency. This is due to the existence of high eutectic fractions at low temperatures, as well as porosity formation associated with bad feeding at the end of solidification. A strong cracking tendency was observed below an Fe content 0.2 wt pct owing to decreased precipitation of the Al6(Mn, Fe) phase. It was found that primary Al6(Mn, Fe) phases lead to early bridging between the grains, which reinforces the alloy during the vulnerable temperature range for hot tearing. Zr and Ti additions weakly enhanced or reduced hot tearing severity, respectively.

Place, publisher, year, edition, pages
2019. Vol. 50A, no 8, p. 3842-3854
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:miun:diva-35940DOI: 10.1007/s11661-019-05290-1ISI: 000473514600040OAI: oai:DiVA.org:miun-35940DiVA, id: diva2:1302224
Available from: 2019-04-04 Created: 2019-04-04 Last updated: 2019-08-09Bibliographically approved
In thesis
1. Problems in the Aluminium DC Casting Process Associated with Melt Treatment Operations
Open this publication in new window or tab >>Problems in the Aluminium DC Casting Process Associated with Melt Treatment Operations
2019 (English)Doctoral thesis, comprehensive summary (Other academic) [Artistic work]
Abstract [en]

The quality of DC cast Al alloys is highly dependent on melt batch composition and impurity level in the molten alloy. The chemical composition and cleanliness of a melt is controlled through the melt treatment operations, carried out while the melt is still in the furnace before casting starts. The present work has studied some of these operations and associated problems such as slow dissolution of alloying elements, non-reproducibility in chemical composition analysis and inclusions.

 The results of the dissolution of the alloy elements Mn and Fe showed different behaviors.  For Mn three intermediate phases were involved, all of which exhibited a smooth interface between Mn and the liquid. These three phases were identified as the γ2, Al11Mn4, and µ phases, which grow slowly towards the dissolving Mn particles. The results from the Fe dissolution revealed that only one phase dominates the process, Al5Fe2, which penetrates the Fe particles with an irregular interface.

The interaction between Mn and Ti additions to AA3003 alloys and consequences for the solidification and precipitation behavior was investigated. The study could map the limits for formation of an earlier unknown AlMnTi phase, which formed large particles, detrimental for subsequent rolling operations.

Different sampling procedures for chemical composition analysis were studied, and a novel approach was proposed. A mould with an insulated periphery provided one-dimensional solidification, which gave compositions close to nominal.

 Inclusion distributions along as-cast billets were studied as a function of different holding times, and thus different grades of sedimentation. Holding times longer than 30 minutes did not show any improvements.  It was also shown that if melt remaining in the furnace at end of casting is less than about 3000 kg, the sedimented inclusions are stirred into the bulk again, and can enter into the end of the billet.

The impact on hot tearing susceptibility of different Cu and Fe contents for AA3000 alloys was studied. Cu contents in a range from 0.3 to 1.2 wt%  significantly increase the hot tearing tendency, which was attributed to bad feeding at end of solidification. Decreasing of the Fe content below 0.2 wt%, gives a strong cracking tendency, owing to decreased precipitations of the Al6(Mn,Fe) phase, which contributes to early bridging and thus reinforcement between grains.

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University, 2019. p. 67
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 294
National Category
Materials Engineering
Identifiers
urn:nbn:se:miun:diva-35937 (URN)978-91-88527-89-9 (ISBN)
Public defence
2019-04-25, M102, Holmgatan 10, Sundsvall, 13:00 (English)
Opponent
Supervisors
Note

Vid tidpunkten för disputationen var följande delarbeten opublicerade: delarbete 6 (inskickat).

At the time of the doctoral defence the following papers were unpublished: paper 6 (submitted).

Available from: 2019-04-04 Created: 2019-04-03 Last updated: 2019-04-04Bibliographically approved

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Razaz, GhadirCarlberg, Torbjörn

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