Text 4b. Laser welding of aluminum alloys

Read the following report and write out 10 key words in the right hand box covering the main ideas of the text.

	Aluminum alloys	Key words
1	Application :
2	The welding problems :
3	The ways of overcoming the problems :
4	Advantages of welding :

1. The greatest recent drive towards use of aluminum-based structures has arisen mainly from the automotive industry (e. g. Audi A8, new Audi A2). The requirement for reduced vehicle weight has led to the development of aluminum frame structures (assembled from cast and profile materials), aluminum alloy sheet assemblies and the use of lightweight cast components.

2. Aluminum alloys are used in a wide range of industrial applications because of their low density and good structural properties. Laser welding has been identified as a key technology that can offer distinct advantages over conventional joining techniques such as TIG, MIG (tungsten and metal inert gas, respectively), resistance spot welding, mechanical fasteners and adhesive bonding.

3. The main problems associated with laser welding of aluminum alloys in general are the high surface reflectivity, high thermal conductivity and volatilization of low boiling point constituents. These and other material-related difficulties can lead to problems with weld and HAZ cracking, degradation in the mechanical properties and inconsistent welding performance.

4. These problems are now largely overcome with the advent of higher average powers, improved beam qualities giving a power density high enough to produce a stable keyhole for welding. At present, both CO₂ and Nd:YAG lasers can be used successfully for welding a vast range of aluminum alloys, with slightly higher welding speeds achievable for Nd:YAG lasers compared with similar power CO₂ lasers, because of shorter wavelength (1.06 mm) and improved coupling.

5.Although no special surface treatment is required when welding aluminum, care has to be taken to avoid excessive porosity. Good quality welds can be achieved for most alloys by cleaning the surfaces prior to welding and adequate inert gas shielding of the weld pool.

(1938 characters )

Notes:

HAZ cracking –  heat - affected zone of welds containing local  brittle zones

Nd:YAG lasers - solid-state lasers based on neodymium-doped YAG (yttrium aluminum garnet) crystals

Exercise 11 Read the text and give reasons why the welding is well suited for the automotive industry.

Model : Laser welding is well suited for the automotive industry, because :

1)

2)

High speed laser welding for automobile exhaust components

Arc welding has been the traditional technique for the joining of many automobile parts and components of steel. The advent of laser beam welding with its rapid speed and relatively low thermal distortion has resulted in the erosion of gas metal arc welding (GMAW) and gas tungsten arc welding (GTAW) dominance. The faster joining speed that can be achieved with laser beam welding is particularly suited to the high-production rate requirements in the automobile industry.

Some automotive exhaust components use 409 stainless steel and are currently arc welded. Welding speeds obtained with GMAW or GTAW are usually <2.5 cm/s. Weld speeds that can be achieved with high power laser beam welding can be significantly higher. Consequently, higher production rates can often be expected.

Exercise 12. Render the following text into English.