Bicycle frame made of aluminum alloy 6061

Aluminum alloys for bicycle frames

several aluminum alloys used for manufacturing bicycle frames. Most often they are made of

  • aluminum alloy 6061 (аналога нашего АД33) and
  • aluminum alloy 7005 (аналога нашего 1915),

less of

  • alloys 6066, 6069 and 6013, and
  • high, but difficult to weld aluminum alloys 2014 and 7075 - domestic analogues AK8 and V95.

Встречается в Сети и китайская реклама: «трубы велосипедные из алюминиевого сплава 6063-Т5».

Aluminium alloy 6061

Aluminium alloy 6061 - a complete analogue of the good old AD33 domestic alloy according to GOST 4784, as, however, and abortion 7005 - an analog of our 1915. Alloy 6061 – a standard structural alloys, one of the most popular alloys 6xxx series, after the alloy 6060 and 6063, of course. Its value for a fairly high strength properties, high viscous characteristics and good weldability.

How to make bicycle frames

Let us consider the technology for production of bicycle frames made of aluminum alloy 6061. Она включает пять основных технологических переделов:

  • прессование и порезка в размер труб-заготовок;
  • формование;
  • подрезка труб «на ус»;
  • аргонно-дуговая сварка труб в раму;
  • thermal treatment of the frame on the state T6.

Compression of the alloy pipes 6061

Исходные трубы для рамы изготавливают методом прессования (экструзии). Extruded tubes may be seamless and "seaming". Since none of the manufacturers does not indicate, which is the tube, the, probably, they just "suture", cheaper.

Seamless tubes are manufactured from hollow preforms or when pressing solid preform stitch needle-mandrel. These pipes are truly "seamless", because they do not have any hidden longitudinal seams.

"Seaming" pipe made of solid workpiece to special matrixes, чаще всего типа «портхол» (porthole). In this matrix the metal stream is divided into an inner mandrel into four streams, which are then output from the matrix before joined to form four longitudinal welds. Although they are called welds, no conventional welding there, of course, not. This - the so-called compression welding, which occurs under high temperature and pressure with a special metal welding chambers matrix. Correctly and efficiently performed welds absolutely not visible and the strength properties practically do not differ from the base material.

Forming aluminum tubes

После операции формовки исходно круглые трубы получают более сложную и более «прочную» геометрическую форму: овальность сечения, variable wall thickness of pipes and the like.

Овальную форму обычно получают технологией гидроформинга: помещением трубы в специальную матрицу и закачкой внутрь ее под высоким давлением воды или масла.

Баттинг (от английского «butting») – это утолщение стенки трубы в критических сечениях и утонения – в мало нагруженных. Produced by cold drawing – knurling inside pipe special mandrels.

Trimming aluminum tubes "miter"

In order to easily and reliably weld the frame tubes need to be "tricky" and precisely trim. After such trimming the two pipes are joined with each other completely without a gap. It is on special machines, which provide a clean and precise cut.

Welding of aluminum tubes

To connect pipes clipped into a single structure most commonly used welding, for pipes made of aluminum alloy 6061 - argon-arc. When the argon-arc welding the necessary heat is obtained between the non-consumable tungsten electrode and the work piece. To prevent oxidation of the welding zone an inert gas is used, argon. Argon arc welding is well suited for welding thin-walled tubes and, Moreover, it gives a neat welds. For welding alloy 6061 most commonly used welding wire from the alloy 4043 (в международном обозначении) с содержанием кремния около 5 %, domestic analogue is a welding alloy SvAK5 GOST 4784.

Welding heat-affected zone

The main consequence of a change in welding the physical properties of the base metal and the weld due to heating in the weld zone. In this small zone near the weld, which is called the heat affected zone, It occurs the greatest degradation in mechanical properties, in particular, fatigue strength.

Strong heating causes a change in the aluminum alloy structure - growth of secondary phase precipitates. This coarsening of precipitates reduces the strength characteristics of the material, such as tensile strength, on 30-35 %. for instance, If the tensile strength of the alloy 6061 before welding was about 310 MPa, after welding it decreases to 185 MPa.

alloy frame Heat Treatment 6061

After that, as a welded frame, subjected to heat treatment for restoration of mechanical properties of the alloy is thermally hardened 6061, that have been lost during welding. Typically, this heat treatment on the condition of T6. Она состоит из трех этапов:

  • нагрев под закалку: нагрев до 530 ° C with an exposure of about 1 hours to obtain the solid solution alloying elements of aluminum, in the case of aluminum alloy 6061 – магния и кремния;
  • закалка: быстрое охлаждение до комнатной температуры для задержки легирующих элементов в твердом растворе;
  • искусственное старение: нагрев до 175 ° C with holding for 8 hours to extract fine precipitates dispersed strengthening phase.

After such heat treatment state T6 receives alloy and aluminum alloy full designation 6061 принимает вид: 6061-Т6.