Towards a new standard for a better control

The uses of extruded products are many and well known. The further use of these products surely involves the problem of quality control and consistency of the main technological and practical characteristics. In many cases, the quality of extruded products is the result of the management of the technological process and the characteristics of the billet used. Despite the criticality of this aspect today there are no standards allowing billet producers or extruded product manufacturers to formulate the supply and control specifications correctly in terms of raw material quality. Currently, there are only specific studies and individual specifications between companies. To fill this gap, UNIMET (UNI’s associated body for non ferrous metals standards) activated a specific Workgroup, comprised of foundry and extrusion experts, which has begun the preparation of a new Standard for the quality of extrusion billets.
The activity is being organized in two main sections:
- assessment of the quality control system currently used for extrusion billets, conducted at the main billet supply companies and extruded products manufacturers
- establishment of criteria and preparation of the standard.

Assessment of the quality control system used for the extrusion billets
The assessment was conducted through interviews with experts of each company and the completion of a questionnaire aimed at gathering the following information:
- Type of company (number of employees, annual turnover, annual production and type of products)
- Market and type of extruded products (product sectors, final market, alloys most commonly used)
- Billet production method (for billet manufacturing companies)
- Quality control methods for the characterization of the billets
- Customer relations (existence of collaboration agreements aimed at the resolution of possible issues resulting from defective billets which in some way facilitates quality control activities and increases the quality standards of production, estimate of the percentage of rejected billets and extruded products during production).
The questionnaire was completed by a group of companies that collectively produce more than 130,000 tonnes/year of extruded products, that is approximately 25% of Italian production. The aforementioned extruded products are destined for the sectors listed in the previous table. The sector with the most significant usage is architecture/building (window and door frames, building facades, pipes for systems and structures) with 37.5%, followed by mechanical (precision components or bars), furnishings and transport sectors.
The most popular alloy for extruded profiles among the companies surveyed is without a doubt the 6060 alloy of the 6XXX series, with 65.2% of the total assessed production, followed by 6063 (11.3%), 6082 (8.7%) and 6005 (5.3%).
The situation is summarized in Table 1. Figure 2 illustrates the main quality controls conducted on billets by the companies surveyed. The diagram represents a simple arithmetical percentage of the data collected from the companies with the questionnaire; it can be seen clearly that all the companies interviewed subject billets to quality controls of their surface and dimensional controls, like the angle of inflection, ovalization and roughness.
The other types of controls appear in different percentages depending on the company.

The structure of the new standard
The objective of the new stand ard is to describe methods and procedures for the quality evaluation of aluminium alloy billets for extrusion. Although the types of aluminium alloys for extrusion are quite broad (alloys belonging to the 1000, 2000, 3000, 5000, 6000 and 7000 series), the standard is specifically developed for the evaluation of quality of the 6000 series which is currently used in more than 90% of the production of extruded products.
The standard starts by indicating the most common defects of aluminium billets for extrusion, that is those related to proportion and shape as well as those found internally or externally, for example porosity, roughness, blowholes, inclusions, segregations, shrinkages, cracks.
Regarding these flaws, the standard suggests to conduct quality controls of aluminium billets for extrusion by evaluating the following items:
1. Surface defects: alterations, heterogeneous deposits, solidification defects
2. Internal defects: porosity, discontinuities (cracks, heterogeneous inclusions)
3. Macrostructural characteristics: granular structures, external lack of homogeneity
4. Microstructural characteristics: external segregations, morphology, distribution and nature of intermetallic materials, degree of homogenization
5. Non-destructive testing
Each method is described briefly, explaining the operation principles, operational procedures and fields of application.
Finally, the standard lists the information that the manufacturer of billets for extrusion and the extruded products manufacturer should exchange to guarantee adequate quality control of billets and consequently obtain high quality extruded products. The preparation of the standard has already begun and it is expected that the final draft will be subjected to examination by UNI in 2010.