ARC Centre of Excellence for Design in Light Metals

In 2008, Monash University and the Aluminium Corporation of China (CHALCO) signed project agreements for the first two foundation projects within ICLAR:

Development of Advanced Al-Mg-Si(-Cu) Alloy Technology for Automotive Body Panels (6xxx)

High Strength 7xxx Series Aluminium Alloys with Improved Damage Tolerance (7xxx)

ICLAR is headed by Prof Barry Muddle and these two projects, funded by CHALCO to a total value of A$2.3 million over three years, are the first two projects to be launched under ICLAR. The project structure at Monash University is defined as outlined below.

In March 2009, a delegation from Monash University travelled to some key CHALCO sites in China to familiarise themselves with CHALCO, the key people at the various sites and the project requirements.

March 2009: The delegation from Monash pictured in Suzhou (left) together with Dr Fuan Guo from the Suzhou Institute for Nonferrous Metals Research (SINR) on the right hand side. Dr Guo manages all technical aspects of the collaboration from the CHALCO side.

Delegations

March 2009: The Monash delegation visiting the South-West Aluminium (SWA) Company in Chongqing

Delegations

March 2009: The Monash delegation visiting the North-East Light Alloy (NELA) Company in Harbin

Some pictures from this trip are shown at right.

In 2009, two visiting researchers from CHALCO spent the year at Monash:

Mr Hao Zhong from SINR, working on the formability of 6xxx alloys (Project 1), and

Ms Hua Chen from SWA, working on the homogenisation of as-cast 7150 (Project 2).

Late in 2009 it was confirmed that Mr Hao Zhong and Mr Yong Zhang will commence their PhD studies at Monash University in early 2010.

These will be related to Project 1 (6xxx) and Project 2 (7xxx), respectively.

Development of Advanced Al-Mg-Si(-Cu) Alloy Technology for Automotive Body Panels (6xxx)

The broad targets for this project are defined as follows:

Short term (~1 year): Understand the natural ageing, pre-ageing, paint-bake response and forming behaviour of existing 6xxx alloys (especially SINR and SWA alloys).

Medium term (~2 years): Investigate a matrix of new alloy compositions and test them against the main automotive body panel criteria on a laboratory scale and a pilot plant scale.

Longer term (=3 years): Propose a new alloy and associated process for plant trials at SWA.

The natural ageing, pre-ageing, paint-bake response and forming characteristics of a number of existing and potential automotive body panel alloys are being investigated using various transmission electron microscopy (TEM), three-dimensional atom probe (3DAP), electrical conductivity and mechanical property testing methods.

The detrimental effect of natural ageing is illustrated in the figure below, along with some typical 3DAP results that are being obtained for different conditions to improve our understanding of natural ageing and other early stage decomposition phenomena.

It has already been found that a pre-ageing treatment can be employed after quenching to stabilise the properties and reduce the detrimental effects of natural ageing.

In addition, a number of new developmental alloy compositions were prepared and are being tested against the main automotive body panel specifications with the aim of producing a new automotive body panel alloy and related processes for Chalco.

High Strength 7xxx Series Aluminium Alloys with Improved Damage Tolerance

Short term (~1 year): Understand casting crack mechanisms and propose solutions while commencing heat treatment investigations on Chalco 7xxx materials.

Medium term (~2 years): Provide technical solutions to enable NELA to produce 7150-T7751 thick plate to AMS4252B and Alcoa standards.

Longer term (=3 years): Improve the balance of properties (strength, corrosion, fracture toughness and fatigue) in 7xxx alloys by heat treatment, thermo-mechanical processing and/or alloying so as to improve the competitiveness of Chalco 7xxx aerospace alloys.

A significant amount of time was spent characterising the microstructure and properties of thick-plate 7150 at various stages of the T7751 temper. Most notably, it was found that the 7150-T7751 strength and corrosion resistance can be simultaneously improved by dissolving more constituent particles at higher solution treatment temperatures. The accompanying figure illustrates the solution treatment process and the resulting variation in volume fraction of constituent particles and fraction recrystallised. One difficulty encountered is that higher solution treatment temperatures can result in overheating and quench cracking. As a result, appropriate precautions must be taken when heating to and quenching from the solution treatment temperature. Based on results to date, solution treatment temperatures above the AMS2772E-specified range of 471-482°C are beneficial to the tensile and corrosion properties provided that overheating, quench cracking and excessive recrystallisation can be avoided. The effects on damage tolerance will be explored in more detail in 2010.

In addition to the solution treatment work, retrogression and re-ageing treatments have been explored to enable AMS4252B properties to be obtained with various process parameters or process routes, and particle dissolution and overheating during homogenisation of as-cast 7150 has been investigated for different temperature-time combinations. Preliminary SEM investigations of cracking in 7150 DC-cast ingots revealed that either hot cracking or cold cracking or a combination of the two may occur, depending on the conditions. Further work is planned to investigate such cracking phenomena in as-cast NELA materials in more detail in 2010.

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