What is surface defects of aluminum profiles
Extruded aluminum is usually characterized by high quality of its surface. A combination of smooth and flat surface, outstanding optical properties and high corrosion resistance - all this gives aluminum profiles decisive advantages as compared with other metallic materials, for example, steels.
However, the surface quality of aluminum profiles is highly dependent on die design, quality metal workpiece and pressing technology. Therefore, at weak control technology aluminum profiles on their surface can occur various surface defects. Typical surface defects of extruded aluminum profiles are shown in Figure 1.
Figure 1 - typical surface defects
extruded aluminum profiles 
Below we will consider “popular” extrusion of aluminum profiles 6xxx alloys defect, primarily, alloys 6060 and 6063 – defect “pick-ups”.
The name of defect
The English spelling of the defect has various variations:
- pick ups,
- pick-ups (with a hyphen) and
- pickups (слитно).
The combination pick up is used in English to mean the following actions:, hook it up, pick up and so on. P.
This defect has the following German variants of the name :
- Preßsflöhe ("press fleas") – main name;
- Preßfischchen ("press fish");
- Preßabrieb ("press abrasions");
- Klebstellen («nalipy» (?)) [Kleb – glue].
GOST 22233-2018 mentions the following surface defects of aluminum profiles: bubbles, longitudinal traces of the matrix, teaser and adhered, but does not provide any technical descriptions of these defects. Defect, which in English is called pick-ups, and German - Preßsflöhe, apparently, most consistent defect "adhered", though, as will be seen below, this defect is and signs of "galling".
Note, that aluminum presses call this defect differently: "fleas" (like the Germans), "Hedgehogs" and "brush".
Details of the defect
The German catalog of defects for extruded aluminum profiles  gives the following description of the defect of Preßsflöhe (pick-ups):
"Fine particles of aluminum and aluminum oxide, which were taken from the surface of the aluminum profile and later settled again on its surface. Have the form of a comma or a comet, which are oriented in the pressing direction. May occur in conjunction with the defect "longitudinal tracks matrix" ".
In the dissertation , this defect is described as follows:
"Pick-ups defect" looks like broken lines of grooves (scoring), which often [but not always] end in a lump of aluminum particles (sticky), which rises above the surface of the profile ".
A schematic view of the defect “pick-ups is shown in the figure. 2.
Figure 2 – Typical schematic appearance of a pick-ups defect 
Figure 3 – Defect «pick-ups» on the just extruded profile
without additional processing 
More information on the causes of the defect “nalip” and measures to prevent it, see. article in the PAYED CONTENT heading:
1. Storen S. and Moe P.T. Extrusion // Handbook of Aluminum: Vol. 1/ George E. Totten, D. Scott MacKenzie, 2003.
2. Characteristics of extruded aluminum sections surfaces / IWK Aachen, 2001.
3. Surface Quality of Aluminium Extrusion Products / Xiao Ma, PhD Thesis, University of Twente, Enschede, The Netherlands, 2011.
4. Extrusion Defects Fundamentals & Solutions for Optimum Finish/ Jerome Fourmann (Rio Tinto), (AEC Webinar), 2017